Hybrid imaging method to monitor medical device delivery and patient support for use in method

ABSTRACT

This invention discloses a method and apparatus to deliver medical devices to targeted locations within human tissues using imaging data. The method enables the target location to be obtained from one imaging system, followed by the use of a second imaging system to verify the final position of the device. In particular, the invention discloses a method based on the initial identification of tissue targets using MR imaging, followed by the use of ultrasound imaging to verify and monitor accurate needle positioning. The invention can be used for acquiring biopsy samples to determine the grade and stage of cancer in various tissues including the brain, breast, abdomen, spine, liver, and kidney. The method is also useful for delivery of markers to a specific site to facilitate surgical removal of diseased tissue, or for the targeted delivery of applicators that destroy diseased tissues in-situ.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.10/916,738, filed Aug. 12, 2004, which claims the benefit of U.S.Provisional Application No. 60/506,784, filed Sep. 30, 2003.

STATEMENT CONCERNING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

FIELD OF THE INVENTION

This invention relates to the field of medical imaging and particularlyto a hybrid imaging method and apparatus used to monitor and optimizethe placement of interventional medical devices in human tissues.

BACKGROUND OF THE INVENTION

A number of techniques, methodologies, apparatus and systems have beenproposed to improve the accuracy of instrumentality placement such asneedle or catheter placement into tissue based on measurements from 3Dimaging formats. These imaging formats (such as Magnetic ResonanceImaging, sonographs (ultrasound), fluoroscopy, X-ray, and the like)locate the needle entry device in relation to treatment- ortherapy-targeted tissue, such as MR-detected target tissue. Theseimaging formats generate imaging data that are used to determine theappropriate positioning of the needle during treatment, which needletypically is placed in a guide device and moved into the tissue. In manycases, the needle is delivered solely on the basis of this imaging datainformation and confirmation of the final needle position relative tothe target requires a second set of images to be acquired. In caseswhere tissue stiffness variations are extreme, the needle may deviatefrom the desired path and deflect on-route to the target tissue.Similarly, the needle may distort the tissue itself and thereby move thetarget tissue to a new location, such that the original targetingcoordinates are no longer correct. Further limitations of currentsystems include the fact that needle position is often determined byreference to its artifact generated in the MR images. From thisartifact, the operator infers the actual needle position relative to thetarget position. In many situations this is appropriate; however, whentargeting small lesions (i.e. <7 mm), the needle artifact (often 5-9 mm)may obscure the target, limiting the ability to use even real-timeimaging data, as from MRI, to validate needle/target position.

Numerous articles have been published in the medical literaturedescribing imaging methods which can be used to monitor and optimize theplacement of interventional medical devices in human tissues (e.g.,Greenman et al, Magnetic Resonance in Medicine, vol. 39:108-115, 1998;Orel et al., Radiology, vol. 193, pp. 97-102, 1994; Kuhl et al.,Radiology, vol. 204, pp. 667-675, 1997; Fischer et al., Radiology, vol.192, pp. 272-272, 1994; Doler et al., Radiology, vol. 200, pp. 863-864,1996; Fischer et al., Radiology, vol. 195, pp. 533-538, 1995; Daniel etal., Radiology, vol. 207, pp. 455-46, 1998; Heywang-Kobrunner et al.,European Radiology, vol. 9, pp. 1656-1665, 1999; Liney et al., Journalof Magnetic Resonance Imaging, vol. 12, pp. 984-990, 2000; Schneider etal., Journal of Magnetic Resonance Imaging, vol. 14, pp. 243-253, 2001;Sittek et al., Der Radiologe, vol. 37, no. 9, pp 685-691, 1999; Jolesz,Journal of Magnetic Resonance Imaging, vol. 8, pp. 3-6, 1998; Lufkin etal., Radiology, vol. 197, pp. 16-18, 1995; Silverman et al., Radiology,vol. 197, pp. 175-181, 1995; Kaiser et al., Investigative Radiology, vol35, no. 8, pp. 513-519, 2000; Tsekos et al., Proceedings of the IEEE 2ndInternational Symposium on Bioinformatics and Bioengineering Conference,2001, pp. 201-208).

To address limitations described in the published prior art, a means toverify the actual trajectory of the needle is needed. A satisfactorymethod must be capable of observing the target tissue to ensure eitherthat needle deflection or target tissue movements can be incorporatedinto the needle delivery path, thereby ensuring accurate needledelivery. Modified bore design MR magnet systems have been developed toprovide more open access to the patient. As such, imaging and needlemanipulation can take place concurrently with the physician having someaccess to the patient while the patient is positioned in the bore.However, these “open” systems are not always available and are often ofsuboptimal field strength, which can result in reduced image quality.Other proposed solutions in the art involve in-bore robotic devices thatenable manipulation of the needle within the bore of the imaging magnet.While this approach usefully addresses the issues of tissue/needledeflection, it also removes the normally close interaction between theradiologist and patient, which may lead to high levels of patientanxiety.

SUMMARY OF THE INVENTION

The present technology provides a medical imaging system capable ofvarious imaging and interventional tasks based on non-invasivedetection, such as MR-detection, of diseased tissue, with many of theseapplications utilizing a hybrid imaging approach in combination withultrasound imaging techniques. The apparatus and techniques disclosedare combined in a system capable of various imaging and interventionalstrategies that can be utilized for comprehensive treatment protocols,for example, complete breast cancer management. Typically, the devicesare delivered through thin needles (ranging from 20 to 9 gauge sizes(0.81 mm-2.91 mm)) which may either place devices into the tissue orretrieve tissue from a specific anatomical region.

The present technology uses 3D imaging data obtained by conventionalnon-invasive imaging techniques, particularly MRI (magnetic resonanceimaging), US (ultrasound), positron emission tomography (PET),computerized tomography (CT), or other three-dimensional imaging system.The technology discloses a number of imaging and interventionalfunctions required for complete breast-MRI patient management, includingscreening for breast cancer, determination of tumor extent andmulti-focality of previously diagnosed cancer, and diagnosis ofsuspicious lesions. Further applications of the technology includeMR-guided positioning of wires and marking devices in the breast tofacilitate any treatment or diagnostic procedure, such as thoseincluding but not limited to surgical excision/biopsy, MR-guided corebiopsy for lesion diagnosis without surgery, and MR-guided and monitoredminimally invasive therapy to destroy diseased tissue. Multi-modalityMR/US breast imaging disclosed in the descriptions of the presenttechnology enables a more effective means of interventional devicepositioning (more accurate, faster, less invasive to the patient), ameans of tissue diagnosis without biopsy (through ultrasound (referredto herein as “US examination”), and a means of monitoring tissueablation boundaries when performing minimally invasive therapies.

While the method of the present technology was specifically optimizedfor breast cancer management, it will be understood by those of ordinaryskill in the art that the techniques and apparatus of this technologycan be easily adapted to various other body parts and pathologies.

One aspect of the present technology is to provide a patient physicalsupport system, including patient support and transport stretcher thatis designed in such a manner to enable maximum access to one or bothbreasts by the operator.

A second aspect of this technology is to provide a compression systemwith four or more independently movable plates designed to avoidinterference with US examination transducer and biopsy needle delivery.“Four or more” may limit bilateral-only implementations

A third aspect of the present technology is to provide a transportstretcher or gurney to aid patient access to the interventional area,the apparatus to include a bridged interventional gap, IV (intravenous)poles which accompany the patient during the entire procedure, aheadrest which accommodates the patient's arms and permits a view out ofthe magnet, and mirrors and lighting to help better position thepatient.

A fourth aspect of this technology is to provide breast compressionplates with various apertures and fixtures to accommodate various MRimaging coils or other radio frequency devices, USexamination-transparent imaging plates, device guide plugs with straightor/and angled orientations, a goniometer system for needle positioning,US examination transducer positioning system, and freehand transducercalibration system.

A fifth aspect of the present technology is to provide software tocalculate needle trajectory based on fixed fiducial positions, to enablemultiple targeting, and to determine a shortest distance to lesion.

A sixth aspect of this technology is to provide additional software tocalculate angled needle trajectory based on fixed fiducial positions, toenable multiple targeting through multiple incisions, to enable multipletargeting though a single incision, to determine a shortest distance tolesion, and to determine any potential interference of needle handlewith surrounding apparatus.

A seventh aspect of the present technology is to provide software for USexamination transducer delivery based on fixed fiducial positions, toenable multiple targeting, to determine shortest imaging distances tolesion, to recalculate with transducer in two orientations, torecalculate with transducer at various angulated orientations, and toconvert tracked transducer coordinates to corresponding stereotacticframe coordinates.

An eighth aspect of the present technology is to provide stilladditional software to convert MR-data, set scan plane and distance totarget.

A ninth aspect of this technology is to provide additional software forvarious MR/US image co-registration, visualization, and image processingtasks

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a shows the stretcher and patient support attached to the MRimaging system according to the invention; b is a side-view of thestretcher with patient in the ‘arms back’ position.

FIG. 2 a shows the patient support structure without sternum orcontralateral breast support. b shows the support structure withattached breast constraint and sternum support, which is angled so as toprovide good medial access to the breast. c and d show the ability toaccess various positions in the breast with various interventional probeorientations with respect to the patient support structure andcompression plates.

FIG. 3 shows the extra interventional volume provided by an opening inthe stretcher according to the invention. a shows one aspect in whichthe member bridging the opening may fold down into the volume. b showsanother aspect in which the member may roll under the patient support inthe stretcher. c shows that the member may also break into multiplesections that may swing laterally and out of the way. d shows anotheraspect in which a portion of the patient support member may lower toprovide an accessible volume. e shows another aspect in which the frontand rear sections of the patient support raise in order to provide anaccessible volume. f shows another aspect in which a slim support with agap smaller than the support wheelbase distance ensures one wheel on thehead end of the apparatus is always in contact. g Shows another aspectin which a bridge support that may move either to the right or left sideallowing medial access to the breast while ensuring the wheels are incontact with the stretcher support surface h Alternatively, sections ofthe stretcher may be removed to permit increased access to the breast.

FIG. 4 shows how the patient support structure may be cantilevered overthe interventional volume according to the method of the invention. Thisdesign provides for the maximum access to the breast. b shows the shapeof the arches relative to the MR bore. In order to prevent the structurefrom tipping over with a patient in place and separation of the patientsupport from the stretcher, sliding or rolling constraints can beincorporated into the system. c shows various embodiments of theseconstraints. d shows the extension of the arch support structures sothat they form a complete cylinder around the patient.

FIG. 5 shows the plate locking/positioning system of the patient supportand the related apparatus according to the invention. The compressionplates can be moved anterior/posterior within the plate locking support.a illustrates how the compression plates/locking supports can beintroduced from the side of the apparatus. Each plate can be movedindependently and to any position in the left/right direction. b showsthat additional compression plates in the superior/inferior directioncan be accommodated so as to “box” the breast. c shows another aspect ofthe invention whereby various embodiments of rail positions are possibleas well as flexible sling designs to compress the breast against thechest wall.

FIG. 6: illustrates how various compression plate designs may beaccommodated according to the invention. a Attached to the compressionplate are fiducial markers and fixed positions to attach coils andpositioning stages. b Attached to these compression plates (or embeddedwithin) are sets of coils. c The compression plate may be a fenestratedplate for needle access. d The plate may provide an acoustical openingfor US imaging and intervention. e A transducer positioning stage may beattached at a fixed position on any compression plates.

FIG. 7: shows various coil configurations that may be used according tothe invention. a Bilateral imaging application with 4 coil array. bUnilateral imaging configuration with 4 coil array. c Bilateral imagingwith 4 coil array. In order to minimize the interaction between themedial coils, their size has been reduced and one or more RF deviceswhich operate to decouple the medial coils is introduced. These can beattached to sternum support or positioned by attaching to the platelocking/positioning system as shown in d. and e Additional coils may beincorporated at other positions such as within an anterior/posteriorcompression plate, or within the patient support structure.

FIG. 8: shows various interventional compression plates that may be usedaccording to the invention. Different fenestration shapes can beimplemented as illustrated. A unique feature is the addition of a notchto one side of the opening or indexing component to make it asymmetric.This ensures plugs may be positioned into the opening in only oneorientation. A compression plate consisting of a sterile membrane pulledtaut across the frame as illustrated can be used to compress the breastas well can enable needle entry after making a small incision in thesurface.

FIG. 9 illustrates systems for breast biopsy disclosed in the prior artwhich are based on a pair of parallel compression plates to immobilizethe breast and provide means to direct a needle to a lesion based onfiducial marker measurements made in the MR image.

FIG. 10 a shows how a needle holder may be used according to theinvention to allow arbitrary orientations of a needle for biopsy. Afterthe correct orientation is achieved, the gimbal is locked in position bytightening the threaded clamp. By reducing the dimension of the gimbalas illustrated in b the point of rotation is positioned near the skinsurface.

FIG. 11 illustrates some useful aspects of needle orientation geometryaccording to the invention.

FIG. 12 shows a goniometer that may be used according to the inventionto define needle guide orientation.

FIG. 13 illustrates the angulated biopsy procedure according to theinvention.

FIG. 14 shows a combination fenestrated plate and compression membrane.According to the invention, by compressing the breast using acompression membrane with a fenestrated plate that can move relative tothe breast, more of the breast is accessible for needle guidance.

FIG. 15 illustrates the MR-Guided delivery of tumor boundary markingclips according to the invention

FIG. 16 illustrates the MR/US co-registration procedure which can beused according to the invention. The lesion and fiducial markers areidentified using MRI. Based on the MRI information, an US transducer isdelivered to the appropriate position so that the lesion is centered inthe US image using a stereotactic frame.

FIG. 17 illustrates the MR/US co-registration procedure where afree-hand US transducer positioning system may be used. A touch point isused to register the coordinate system of the tracking device to thefiducial marker defined, and therefore to the MR image's coordinatesystem.

FIG. 18 shows different US probe delivery techniques which can be usedaccording to the invention. Using a mechanical stage with 5 degrees offreedom, capable of fixing an US probe horizontally or on edge, allowsaccurate transducer positioning. Important features enable imaging nearthe chest wall (i.e. apparatus and structure do not encumber access tothis region). a shows a frame with open central aperture and embeddedfiducial markers that may be inserted into the compression frame toprovide touch point reference to co-register the tracking system to theimages.

FIG. 19 illustrates some useful features of the US transparentcompression frame according to the present invention. The thin, angledtop support member helps support the patient and the U-shaped supportframe enables full US imaging access to the breast. b, c and d showalternative embodiments of the US permeable membrane with many cut awayopenings.

FIG. 20 shows various MR/US Hybrid biopsy configurations according tothe invention. a shows the breast compressed between two sterile, UStransparent plates. Imaging and intervention occur from the same side. bshows a configuration with one fenestrated plate and one US permeableplate. The needle approaches from the opposite side from US imaging. cshows a plate with larger fenestrations that can be used to introduce atransducer and needle for same-sided imaging and intervention. d showstransducer and needle delivery through the same side using a positioningstage.

FIG. 21 Illustrates various MR/US Hybrid biopsy configurations accordingto the invention. a shows the breast compressed between two sterile, USpermeable plates. Imaging and intervention occur from the same side witha medial approach b illustrates a configuration with one fenestratedplate and one US permeable plate. Needle approach selected opposite sidefrom US imaging. c shows a plate with larger fenestrations that can beused to incorporate a transducer and needle for same-side imaging andintervention. d shows an embodiment with 2 point needle positioningsystem on opposite side to US imaging.

FIG. 22 Shows hybrid device guidance for delivering multiple markers inthe breast to demarcate tumor boundaries using various compression plateconfigurations. According to the invention, this can be performed in ananalogous manner to MR-guided marker placement.

FIG. 23: Hybrid needle guidance for positioning of multiple markers inthe breast to define tumor boundaries demonstrated from the physicianspoint-of-view.

FIG. 24 a According to the invention, hybrid needle guidance can be usedto position tissue ablation probes and monitor therapy progression. Inthis example, a cryoablation probe can be positioned to the center ofthe lesion using hybrid guidance. b shows how reformatted MR images maybe used to define the tumor extent, while US may be used to monitor icethe development of the resultant ice ball.

FIG. 25. Flowchart illustrating the MRI-guided needle localizationprocedure according to the invention.

FIG. 26. Flowchart illustrating the MRI-guided core biopsy procedureaccording to the invention.

FIG. 27. Flowchart illustrating another embodiment of the MRI-guidedcore biopsy procedure according to the invention.

FIG. 28. Flowchart illustrating the hybrid MR/US imaging procedureaccording to the invention.

FIG. 29. Flowchart illustrating the hybrid-guided core.

FIG. 30. Flowchart illustrating the hybrid-guided marker placementprocedure according to the invention.

FIG. 31. Flowchart illustrating the hybrid-guided delivery of tissueablation probes and monitoring of therapy according to the invention.

The foregoing features, objects and advantages of the present inventionwill be apparent to one generally skilled in the art upon considerationof the following detailed description of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The following described technology encompasses a hybrid imaging methodto monitor the placement of interventional medical devices and apparatusthat can be used in such an imaging method and other medical ortherapeutic procedures. The preferred embodiments are described byreference to both the general and specific attributes and features ofthe components of the technology. However, this specification disclosesonly some specific embodiments as examples of the present technology,which are not intended to be limiting in the interpretation of the scopeof the claimed invention of this patent. It will be readily apparentthat variations and modifications may be effected without departing fromthe true spirit and scope of the novel concepts of the invention.

Patient Support Structure and Transport Stretcher

One of the areas of disclosure of this technology is a patient supportand transport apparatus including a structure, gurney or transportstretcher 1 as indicated in FIG. 1, supporting a patient supportstructure 2. This patient transport stretcher 1 and table top patientsupport structure 2 act to support the patient 26 and to immobilize thebreasts 36, while providing a transportation system for carrying thepatient 26 to an MR imaging system 4, as well as providing a stretcher 1and support structure 2 for the patient during imaging which can beattached and detached from the MR imaging system 4 and moved to otherlocations. The patient 26 lies on the patient support structure 2 in theprone position (face downward) and may be advanced feet first into thebore 21 of the MR imaging system 4. The patient's breasts 36 fall intoan opening 19 at the chest level of the patient support structure 2 andthen can be immobilized by compression plates (not shown in this FIG.)in a medial-lateral direction. According to the technology describedherein, the patient support structure 2 has been designed to: 1) provideroom for large breasts to extend into the access volume without touchingthe bottom of the magnet bore 21, 2) optimize room available for thepatient in the magnet bore 21, 3) allow the patient's arms to bepositioned forward above their head or at their sides, 4) provide accessboth medially and laterally to either breast, particularly towards thechest wall, 5) ensure devices with a wide ranges of oblique orientationshave maximal access to all points within the breast, all withoptimization for patient comfort. The design of the present apparatusthus serves a multitude of imaging and intervention functions, with verylittle adjustment of the components. Medial and lateral interventionsand hybrid imaging interventions can be accomplished without priorknowledge of the approach required. The apparatus disclosed by thepresent invention is substantially different from systems currentlyavailable commercially, such as, for example, the equipment made by MRIDevices, and USA Instruments. Systems presented by Su (U.S. Pat. No.6,163,717), Liney et al, “Bilateral Open Breast Coil and CompatibleIntervention Device,” Journal of Magnetic Resonance Imaging, 2000 aredual function breast imaging and intervention systems. These systems layon the MRI bed with no modification to the normal stretcher's table top.As space is limited in an MRI magnet bore, the unmodified tabletoplimits to space available for access to the breast and for the patientin the magnet. None of these systems are used for functions other thanMR imaging or MRI-only interventions and require significant setup timein the MR imaging magnet to convert from an MR imaging to MRinterventional system.

The concept of a specially designed patient support system and stretcheris not believed to have been presented in the prior art. Schneider etal, 2001, presented a modified MR stretcher for the purpose of MRIbreast biopsy. This invention was also presented in U.S. Pat. No.5,855,554. The top support surface was modified to enable more access tothe breast, whereas the bottom part of the stretcher was not modified.Breast biopsy systems presented by S. H. Heywang-Kobrunner, 1999, Kuhl1999, Fischer (U.S. Pat. No. 5,913,863), Cardwell (U.S. Pat. No.6,423,076) all present modifications to the top surface as well, with nomodification made to the stretcher component. These systems compromiseMR imaging capability for improved access to the breast. No integratedsystem has been developed in an attempt to maximize access to the breastby modification of the tabletop and stretcher, and providing provisionsto use the system for imaging, intervention and multiple modalityfunctions. These concepts can be easily transferred to embodimentswherein the stretcher is a non-wheeled structure, or a stationarystructure.

As shown further in FIG. 1 a, 1 b and FIGS. 2 a) and b), in an exemplaryembodiment of the technology described herein, the patient supportstructure 2 consists of a winged structure with no medial or centralstructural members. There is a cervical (shoulders, neck and head)support area 6. The two arches 28 connect the head support 18 and armsupport 25 (cervical section) to the lower patient support 50 (lumbar orthoracic section). The horizontal aspects of these arches 28 arepositioned posterior to the patient's breasts so as to maximize accessto the patient's breasts in a lateral approach. These arches 28 furtherprovide a restraint for the patient's arms when they prefer to havetheir arms at their sides. Another feature of these arches 28 is toensure a strong structural joint between the superior and inferiorportions of the patient support structure 2. The arches can be made aslarge as needed to ensure the required strength and introducing a curvedgeometry to the arches ensures that the arches can be introduced intothe MR imaging bore. In the extreme, these arches 28 could form acomplete cylinder in which the patient would be placed to maximize thestrength of the patient support. Double arch supports have not beenpresented as a means to provide the fundamental support or connectivelybetween the cervical and thoracic sections of the apparatus.

The patient support structure 2 may ramp upward (inferior ramp 27)towards the opening 19, and may slope downward away from the opening 19towards the head support 18 (superior ramp 29). The inferior ramp 27positions the patient 26 so that her pendulant breasts will not touchthe floor of the magnet bore 21, providing a large volume forinterventional access. The superior ramp 29 (if present) provides aregion for the patient's arms to rest when in the arms-forward position(arms above the head). The use of arching members as the primarystructural component to the system, with or without a removable sternumsupport is unique. The geometry presented in FIG. 4, has been designedto provide structural support and patient support so as not to interferewith access to the breast.

The volume available for interventional access is maximized by thetransport stretcher and the design of the table top patient supportstructure 2 to provide an angulated entry geometry to the lateral aspectof the breast volume but creating wide or tapered entry of the tablestructure toward the patient volume from the lateral aspects. The accessprovided by this arch design is illustrated in FIG. 2 a) b), c), d). Abridge section 8 of the transport stretcher 1 provides support when thepatient support structure 2 is being rolled into the magnet bore 21, butis designed to retract out of the way when the patient support structure2 is fully removed from the magnet bore 21 for intervention. In oneembodiment of this technology, a headrest 18 is situated at the superiorend of the patient support structure 2, whose height and angle may beadjusted. Mirrors 40 may be provided below the headrest 18 to allow thepatient 26 a right-side-up view out the front of the magnet. Thisfeature of the technology is intended to reduce patient anxiety. Theembodiment shown has a single telescoping headrest 18 which incorporatesa tilting adjustment to maximize the room available at the superior endof the structure, and to permit adjustment and clamping of the headrestorientation with one hand. A simplistic headrest design has beenpresented by Schneider et al, 1999, however this design does not embodyany additional features described above.

In further embodiments of the technology described herein, bridgemembers may be used to support the patient over the breast accessvolume, as shown in FIGS. 2 a, b), c) and d). For applications involvingboth breasts (i.e., bilateral applications) a sternum support member (44as shown in FIG. 2 b)) may be used. For unilateral applications, abridge member breast support 34 that supports the contralateral breastand compresses it against the chest wall is attached. Unlike the devicedescribed by Heywang-Kobrunner et al., “MR-Guided percutaneousexcisional and incisional biopsy,” European Radiology, vol. 9, pp.1656-1665, 1999, in the present technology, the angle of this supportoptimizes medial access to the breast while supporting the patient in acomfortable position. Angulation of the breast support 34 (10-30degrees) further provides improved access to the breast for medialaccess with an angulated device approach. The embodiment of a removablesternum support member 44 and contralateral breast support 34 maximizesaccess to the breast from medial and lateral aspects and is unique withrespect to the prior art. Removal of the breast and sternum supports areindicated in FIG. 2 a) and b). This resulting improved angulation with abreast support 34 is demonstrated in FIG. 2 c) with the needleapproaching the breast beneath the contralateral breast support 34.Maintaining the sternum support member 44 in place would result in alimited angular access to the breast. Schneider et al, 2001 (E.Schneider, K. W. Rohling, M. D. Schnall, R. O. Giaquito, E. A. Morris,and D. Ballon, “An Apparatus for MR-Guided Breast Lesion Localizationand Core Biopsy: Design and Preliminary Results,” Journal of MagneticResonance Imaging, vol. 14, pp. 243-253, 2001) shows the top portion ofthe tabletop could be rotated to accommodate either left breast or rightbreast access. No attempt was made to improve access to the breast forimaging or interventional procedures as is provided by the systempresented in this document by way of a unique patient support structure2 and optionally removable sternum support member 44 and contralateralbreast supports 34.

Another feature demonstrated in FIG. 2 b and FIG. 2 d is the addition ofa disposable blood barrier 42 that is attached to the patient supportstructure 2. Features at the base of the thorax (thoracic) support 33and the shoulder and neck (cervical) support 31 allow attachment ofvarious blood catchments (plastic diapers). These can be easily attachedand removed during the procedures. A further preferred embodiment shownin FIGS. 2 a and b consists of IV poles 22 at the inferior and superiorends of the apparatus. These poles act to hold the saline drip duringthe breast procedures. No attempts have been made to implement any ofthese embodiments in the prior art.

FIGS. 2 c and d shows a patient support structure with respect tointerventional and imaging probe access. FIG. 2 c (Front View) showsInterventional or imaging probes 30 may be introduced at variousorientations to the breast from either medial or lateral directions.(Note: only a portion of the patient support structure 2 and compressionplates 32 are shown in this view). Arrows indicate range of probe 30positioning without interfering with apparatus infrastructure. FIG. 2 d(Lateral view): Varied access of probes 30 is shown in a side view.Tapered geometry of patient bed (not shown) and positioning ofcompression plate 32 locking mechanisms and rail guides (not shown) farfrom a breast enables large angular and positional access. This taperedgeometry extends to the medial aspect through a gradually slopedcontra-lateral breast support 34.

Transport Stretcher

The transport stretcher 1 is used to transport the patient to and fromthe MR image 4 r, to dock to the MR imager 4 such that the patientsupport structure 2 may be moved to advance the patient 26 into themagnet's bore 21, and as a table for the patient support structure 2during interventional procedures and ultrasound (US) exams, which areperformed away from the MR magnet's field (FIG. 1). The patient supportstructure 2 (e.g., FIG. 2 a)) rolls on the guides of the transportstretcher 1 when advancing into the guides 23 in the bore 21. On theunderside of the patient support structure 2 are a set of wheels (notshown). The cross-section of the patient support structure 2 correspondsto the internal geometry of the bore of the magnet. The transportstretcher 1 attaches (docks) to the connection mechanisms of the imagingsystem 4. The interlocks and safety mechanisms depend on the specificdesign of the MR imaging system 4. In order to have complete access tothe breast when the patient 26 and the patient support structure 2, areremoved from the magnet bore 21, a large section of the transportstretcher 1 can be retracted (FIG. 3 a-d), leaving a large gap. In themethod of this technology, this can be accomplished in a variety of waysas illustrated in FIG. 3 a-d). The patient support structure 2 will besupported across this gap and not be in a full cantilever position atany time (i.e., wheels on patient support structure 2 will always be incontact with a surface on the transport stretcher 1 or MRI bore 21 whenthe patient support structure 2 is moving in or out of the bore 21). Inorder for this to be accomplished, there are a variety ofembodiments. 1) A member (e.g., 56) that folds up from either the torso,or the head end of the stretcher. 2) A member (e.g., 72) that pulls outfrom under the torso end of the stretcher, 3) Two members (e.g., 68)that split apart and hinge out laterally. The gap 57 in the structureprovides additional interventional volume. Additional embodiments mayalso include side walls 58 that match the geometry of the magnet. Thisprovides the operator with a means of verification that needlesextending from the breast will not hit the side of the magnet as thepatient is returned into the magnet for any additional MRI scanning. Asthe large interventional access area is unique to this invention,mechanical provisions to enable use of this additional space withoutcompromising patient safety, or complexity for the operator as presentedin this document are unique with respect to the prior art.

Additional features of the stretcher may include a set of drawers in theside to organize all the secondary apparatus associated with the system.Further embodiments of this technology may include a set of lights 60 onthe medial/lateral faces of the right and left sides of the breastand atthe bottom of the gap in the stretcher. The orientations and intensitiesof these lights may be adjusted by the technician or radiologist.Another embodiment may be an adjustable mirror 62, or a mirrorpositioned on the lower part of the apparatus that allows theradiologist to more easily see the position of the nipple when thebreast is compressed. This is a desirable feature in the method of thetechnology described herein, because the nipple is often used as animaging landmark in the breast, and uneven compression may cause it todeviate either medially or laterally, thereby providing an unreliablelandmark. These features of the present invention are shown in FIG. 3a-d.

In FIG. 3 d, the stretcher is shown with the telescoping bridge 64 beingelevated into support position.

FIG. 3 e shows that the entire stretcher, with the exception of thebridging 65 can be raised or lowered to provide a flat surface whenadvancing the patient support into the bore or to provide a gapfacilitating device delivery and intervention.

FIG. 3 f shows that the stretcher may have a slim support 66 with a gapsmaller than the support wheelbase distance, which ensures one wheel onthe head end of the patient support is always supported

FIG. 3 g shows a stretcher with a bridge 69 that moves left or rightallow medial access to one or the other breast.

FIG. 3 h shows a patient stretcher with a removable section 70 and thearea from which it has been removed 71. This allows medial access to thebreasts while assuring that the patient support structure 2 is incontact with the stretcher support surface 1.

FIG. 4 shows another embodiment of a transport stretcher 78 and acantilevered patient support structure 77 which provides patient supportin a full cantilever position based on stronger arched members,adjusting the mass distribution of the apparatus to move the center ofmass towards the inferior end of the bed and the addition of sliding orrolling constraints in the transport stretcher and magnet bore as neededto ensure the patient support cannot tip from the transport stretcherduring patient manipulation. An example of appropriate tabletopconstraints are illustrated in FIGS. 4 a, b, c and d. In the context ofa cantilevered design, the shape of the cantilevered patient supportstructure 77 and the arches 28 ensure rigidity of the support and itsstability on the transport stretcher 78 while carrying a patient load.As illustrated in FIG. 4 d, the arches 28 may be extended around theposterior of the patient to form a continuous or near continuouscylinder. This extension of the arches provides a continuous geometrythat is extremely rigid and appropriate for a cantilevered patientsupport strategy.

In FIGS. 4 a and 4 b, the cantilevered patient support structure 77 maybe cantilevered over the interventional volume 76 as indicated. Thisdesign maximizes access to the breast (not shown). In order to preventseparation of the cantilevered patient support structure 77 from thetransport stretcher 78, sliding constraints 79 are incorporated toprevent tipping. Also indicated in FIG. 4 a, is the addition ofpositional tracking devices 80 into the body of the stretcher. Removablehandles 81 ensure full access to breasts (not shown).

In FIGS. 4 b and 4 b 1, the matched fit of the curved arch 83 into thecurve of the MRI bore 85 is shown.

This cantilevered approach of FIG. 4 provides the maximum real-estateand access in the vicinity of the breast for ancillary instrumentationsuch as US (ultrasound) imaging probes, therapeutic devices andpositioning systems and to maximize access to the breasts from medial,lateral, superior-inferior or oblique directions for breast manipulationor interventional procedures. Also present may be an embedded positionaltracking system. By integrating a positional tracking device into thestretcher (not restricted to, but including optical and magnetictracking devices) at a position that provides line-of-sight, orreasonable proximity to the interventional volume t enables orsignificantly simplifies the procedures discussed further in thisdocument.

FIGS. 4 c 1, c 2 and c 3 show alternative linear guides for the patientsupport guides. In FIG. 4 c 1, a tongue 90 in the transport stretcher 78fits into a groove 92 in the patient support structure 77 to preventrotational movement. In order for the cantilevered patient supportstructure 77 not to overturn during patient transport, it is necessaryto constrain the motion of the patient support structure 77 to move inand out of the bore of the magnet 85 (S/I patient orientation). Somepossible alternative embodiments of motion constraints are illustratedas FIG. 4 c 2 and FIG. 4 c 3.

FIG. 4 d shows a modification of the arch structure 91 of thecantilevered design. The arches 91 in this illustration have beenextended to form a complete cylinder around the patient. The openingprovided in the arch structure 91 still enables access to the breast inthe manner illustrated in FIGS. 2 c and 2 d. The degree to which thearches are extended around the patient is dependent on the structuralstrength deemed appropriate. Furthermore, the opening of the arch 91 maybe widened in the Superior/Inferior direction resulting in more accessto the breast at the expense of a relatively weaker structure.

FIG. 5 a (1 and 2)-c shows only the plate locking system 104 of thepatient support 100 and the related apparatus. The compression plates102 can be moved anterior/posterior within the plate locking support104. The compression plates/locking supports 104 can be introduced fromthe side of the apparatus. FIG. 5 a 1 is a side view and FIG. 5 a 2 is abottom view. Each plate can be moved independently and to any positionin the left/right direction. Additional compression plates in thesuperior/inferior direction can be accommodated so as to “box” thebreast. In FIG. 5 b, are shown height adjustable plates 112 and a guide116 for the anterior-posterior compression plate that slides left andright. Various embodiments of rail positions that are possible are shownin FIG. 5 c, as well as flexible sling 124 designs to compress thebreast against the chest wall. Alternative locations for plate lockingguide rails 120 are also shown.

Compression System

Each breast is compressed in the medial-lateral direction by a pair ofcompression plates 102 that are in turn held in place by a pair of platelocking supports 104 (FIG. 5 a 1, 5 a 2, 5 b, 5 c). “Compression plates”may have a number of different designs as described in the practice ofthis technology. Two or four compression plates may be used at a timedepending whether unilateral or bilateral applications are beingperformed. The plate locking supports 104 may be constrained to movealong linear guides in a medial/lateral direction. They may be free tobe removed completely or added from the left or right sides of thepatient support structure 100 while the patient is lying on it. Theheight of the compression plates 102 in the anterior-posterior directioncan be adjusted along a linear guide fixed to each plate locking support104. The compression plates 102 likewise can be added or removed fromthe plate locking supports 104 from the top or bottom, though only fromthe bottom when the patient is above them. Both plate locking supports104 and compression plates 102 are continuously adjustable across theentire range of their support, do not interfere with one another and canbe locked in place. The system illustrated in FIG. 5 a-c shows two guiderails 120 to support the compression plate 102. With two guided rails onone side, this provides a completely open geometry toward the oppositeend of the compression plate 102 to maintain greatest access. However,with such a geometry, the compression plate 102 may not demonstrateadequate rigidity that can be overcome by placing one guide rail at theopposite end of the compression plate 102. Similarly, using multipleguide rails placed at each end of the compression would further stiffenthe system. In these figures we have illustrated the guide rails to berods and the compression plates 102 are fitted on the guide rails withlinear bearings. Multiple configurations are possible, including the useof T slots and dovetails as dictated by the space available for thesemounting structures. The locking mechanism for the compression plate 102could be formed by a simple cam mechanism or ratchet and pawl structurewhich allow the use of one hand to both secure (lock) and position thecompression plates 102. The positioning of plate-locking guide rails 120can be variously positioned as shown in FIG. 5 c.

Rail systems and tongue-and-groove compression plate support systemshave been presented in the prior art. The design presented by Kuhl,1997, demonstrates a dual rod system. This design differs significantlyfrom the presented embodiments in that the medial and lateral plates cannot be independently positioned, there is only provision for access toone breast at a time, and both plates can not be removed with thepatient on the apparatus. Other designs presented in the prior artincluding U.S. Pat. No. 5,913,863, U.S. Pat. No. 5,855,554, U.S. Pat.No. 6,423,076 do not detail the compression apparatus, or demonstratelimited ability to position the plates as described by Kuhl 1997 (C. K.Kuhl, A. Elevelt, C. C. Leutner, J. Gieseke, E. Pakos, and H. H. Schild,“Interventional breast MR imaging: clinical use of a stereotacticlocalization and biopsy device,” Radiology, vol. 204, pp. 667-675, 1997)and Heywang-Kobrunner 1999. (S. H. Heywang-Kobrunner, A. Heinig, and R.P. Spielmann, “MR-Guided percutaneous excisional and incisional biopsy,”European Radiology, vol. 9, pp. 1656-1665, 1999.)

Another aspect of the present technology enables compression of thebreast in the anterior/posterior direction. This is a particularlybeneficial feature because US imaging and interventional procedures areoptimized by increased breast contact with the compression plates.According to this technology, this can be accomplished by compressingthe breast into a box-like shape as illustrated in FIG. 5 c. U.S. Pat.No. 5,706,812 to Strenk et al. discloses an inflated bladder whichimproves access to the breast during US imaging. However, unlike thepresent technology, the invention disclosed by Strenk et al. does notprovide for equivalent access to the lateral and medial sides of thebreast during imaging and interventional procedures. This concept may befurther extended to include rods, pointers, convex or concave surfaces,or the like that are attached to the compression plates and/or thepatient support structure that perform the function of improving breastcontact with the compression plates.

Another feature of the present technology is the ability to move andlock the medial and lateral plates independently through the platelocking supports using just one hand. This enables the operator tocompress the breast with one hand, while locking it in place with theother. The ability to adjust the positions of the plates along theentire width of the bed is a useful feature which accommodates thevarious sizes of patients and various clinical applications (e.g.medial/lateral interventions, bilateral imaging). Another further aspectof the invention enables movement of the plates in the verticaldirection during compression. This allows the operator to position theplate as close to the chest wall as possible. In the method of theinvention, compression plates inserted into the plate locking supportsmay take different forms as described in the following section of thisspecification. The present technology provides a method to quicklyinterchange plates for various functions by vertically loading theplates into the plate locking supports. Furthermore, compression platesmay be introduced or removed with the patient still on the apparatus byway of removal or addition of the plate locking supports (FIGS. 5 a 1and 5 a 2).

Compression Plates

According to the present technology, numerous functions are accomplishedusing various types of compression plates. These functions include:

1) MR imaging coils: various coil arrays—single or multiple percompression plate.

2) Interventional plates: multiple hole plates, fenestrated plate asshown in FIG. 6 c, 8 (with various aperture shapes)

3) US-transparent membrane and membrane support frame which is

-   -   a. Reusable for imaging    -   b. Can be sterilized    -   c. Can be cut to allow incisions in the breast    -   d. Tension adjustable to adjust flexibility and conformation

The compression plates also holds a breast immobile while a fenestratedplate in contact with it is moved

The plates disclosed by this invention can be sterilized and can holdseveral fiducial markings 140 (e.g., FIG. 6 a) visible on MRI which actas reference points between the MR images and the physical space. Theplates can also have attachment points for MR imaging coils (FIG. 6 b),needle positioning apparatus (FIG. 10 a and 10 b) and US transducerpositioning systems (FIG. 6 e). The design and function of these plateswill be discussed in detail in a subsequent section of the specificationin the context of their clinical use. A plurality of compression platesthat may be used according to the technology are identified on FIG. 6 a,6 b, 6 c. The compression plates may be positioned at any of the 4compression points (left medial, left lateral, right medial, rightlateral) on the breast in any combination required. FIG. 6 c showscompression plates with fenestrated plates 146. FIG. 6 e shows atransducer 148 and a positioning stage 150. These coils can beinterchanged in a modular fashion to maximize and optimize the numberand types of coils used, whether for unilateral or bi-lateral imaging orintervention. Modular coils may also provide either large or small coilsof various designs, RF shields, and coils for different field strengthand field shapes.

FIG. 7 shows various coil configurations a, b, c, d, and e from an axialview of a patient on the apparatus. a) shows a Bilateral imagingapplication with 4 coil array. b) shows a Unilateral imagingconfiguration with 4 coil array. c) shows a Bilateral imaging with 4coil array 160. In order to reduce coupling between the medial coils,their size has been reduced and an RF-shield has been inserted (attachedto sternum support) to limit coil interactions. This shield may take avariety of forms all with the same purpose—passive medial coildecoupling. d) shows RF-shields have been attached to the medialcompression frames. e) shows that Coils may also be attached to the A/P(anterior/posterior) compression plate and used with any of theaforementioned coil geometries. In all cases the maximum number ofallowable coils, for the maximum number of data collection channelsshould be used. A sternum support 162 is also shown, as well as asternum support with RF shield 164, and RF-shields attached to themedial compression plates 166.

Imaging Coils

MR imaging coils are considered in this technology. In one embodiment,the coils may be incorporated into the system by being embedded into thecompression plates as by way of non-limiting examples, using fixtures122 for coil attachment in FIG. 6 a. In another embodiment, the coils138 may be attached to the outside of the interventional or UStransparent plates 142 as shown in FIG. 6 d. In another embodimentadditional coils may be embedded into the patient support structure. Inanother embodiment, the coils may be positioned as close as possible tothe breast in order to produce higher-quality images. The MR coils mayconsist of a single pair of coils per breast (1 medial, 1 lateral), oran array (more than two coils, multiple pairs of coils) per compressionplate. Further enablement for coil configurations per se may be found inSchneider et al., “An Apparatus for MR-Guided Breast Lesion Localizationand Core Biopsy: Design and Preliminary Results,” Journal of MagneticResonance Imaging, vol. 14, pp. 243-253, 2001, which is incorporatedherein by reference. However in that description, no attempt was made tomaximize the number of coils used for imaging unilateral or bilateralanatomy. As a comparison, in the description provided by Greenman, etal., MRM 1998, no attempt was made to ensure the medial and lateralplates could both be positioned as close as possible to the breastthrough an appropriate compression system to maximize image quality. Inthe present technology, moving the medial coils further from one anotherwould provide reduced coil decoupling and limit the issue of coilinteractions and the complexity of coil switching circuitry.Furthermore, no attempt to substitute coil arrays so as to maximize thenumber potentially used for unilateral or bilateral imaging without hasbeen made.

The present technology can also provide for coils specific to differentsized patients. A different set of coils could be used for needlepositioning sequences than those used for simple imaging. These coilsfor needle positioning would have a large central opening through whichneedles could be placed and would be mounted over top of othercompression plates (e.g. a fenestrated plate and/or US transparentmembrane). According to the invention, these coils would be removableand their positions on the underlying compression plate would beadjustable to ensure clearance from a device being inserted into thebreast.

Fiducial Marker System

In the methods of the present technologies, device delivery may be basedon the use of MR-visible fiducial markers as a reference between MRimages and physical space. “MR Imaging-guided Localization and Biopsy ofBreast Lesions: Initial Experience,” Radiology, vol. 193, pp. 97-102,1994, and Kuhl et al., “Interventional breast MR imaging: clinical useof a stereotactic localization and biopsy device,” Radiology, vol. 204,pp. 667-675, 1997 describe the use of fiducial markers placed at a knownposition on the embedded or attached apparatus. The more referencepoints that are used, the more accurate is the registration of the twospaces (physical/imaging). Various embodiments of the fiducial markersmay be used. The fiducial markers may be embedded into some compressionplates in the apparatus for simplicity. In other structures, such asfenestrated plates which may be moved relative to the breast during aprocedure, the markers may be removable. They may also need to beremovable if they may not be sterilized. Device targeting and trajectorycalculations can be automated if the fiducials are at a known positionon the apparatus. Another embodiment of fiducial marker arrangementsincludes a detachable plate which may be positioned at a fixed positionin the compression frame relative to the fenestrated plate positions(e.g. FIG. 18 a).

MR Breast Imaging

The prior art references indicate that the majority of breast imagingprocedures involve simple contrast-enhanced breast imaging withoutintervention. It is important to have a system that is capable of singleor bilateral breast imaging for screening, diagnostic or surgicalplanning purposes.

According to the present technology described herein, both unilateraland bilateral breast imaging procedures can be performed with the simpleremoval and replacement of compression plates containing coils and coilarrays and the removal and replacement of the central support member(used in bilateral imaging) with various support members. The additionof coil decoupling mechanisms such as coil windings, specially designedconductive layers, and electronically active blocking circuits into thespace between the two coil pairs is enabled by the open architecture ofthe apparatus of the present technology. One embodiment includesattachment of the mechanism (illustrated in FIG. 7 as an RF shield), tothe bottom of the central support member. Quick attachment of thismember enables easy preparation of the system for various imagingpurposes. Alternatively, more than one RF shield could be introduced andmounted on the guide rails to be positioned in a patient-specific mannerto optimize imaging performance. The open architecture disclosed in thisinvention further enables improved access to the breast for the operatorfor breast positioning before imaging. The addition of lighting and amirror system enables visualization of the breast. The ability to seethe nipple and the ability to move the medial and lateral platesindependently facilitates having the nipple pointed downward and in themiddle of the imaging field. This is important as the nipple is used asa reference point for the radiologist. Furthermore, the ability to movethe plates up towards the chest wall ensures optimal compression of thebreast ensuring there is minimal motion during the procedure.

According to this invention, the ability to use different coilconfigurations for different purposes (bilateral, unilateral) and toaccommodate various patient breast sizes (e.g. one set for large, oneset for small breasts) is critical to acquire optimal images. Dependingon the number of data acquisition channels in the MR imaging system,multiple coil arrays can be used. Various coil geometries which may beused in the method of the invention are presented in FIG. 7. Thisconcept of removable coils has not been presented in the prior art withrespect to 1) providing the maximum number of coils for the imagingapplication (bi-lateral, unilateral, interventional imaging) so as tomaximize the number of active data collection channels. 2) Adjustingcoil arrays for smaller or larger breasts, 3) Upgrading coils and coilcabling as the associated MRI system is upgraded for increased number ofdata channels, 4) Providing coils operating at different frequencies forhigher magnetic field applications. The ability to easily remove coilsand exchange them for other coils without modification of the mainimaging structure is a critical feature enabling optimized imaging andinterventional functions with a single apparatus.

MR-Guided Breast Interventions

Various breast interventional procedures are enabled by the apparatusand method of the present invention. The ability to perform core biopsy,wire localization, lesion marker placement, guide tissue ablationdevices and placement of tissue therapy devices (chemotherapy,radiotherapy, cryotherapy, heat therapy, gene therapy) are some of theclinical applications enabled by the invention. Apparatus and techniquescommon to these procedures are presented in the following section.

MR-Guided Device Delivery

The ability to accurately deliver a plurality of needles to a lesion orto multiple sites within the breast using MRI guidance is a fundamentalaspect of the present invention. According to the method of theinvention, fiducial markers can be used as reference points, so that theoperator can position various MRI-compatible needles (e.g. titanium andcomposite needles) ranging from fine aspiration needles (approx 24 gauge(0.51 mm)), to wire delivery needles (20 gauge, (0.81 mm)), toconventional core biopsy needles (16 to 14 gauge (1.29 mm-1.63 mm)),coaxial introducer needles (14 to 11 gauge (1.63 mm-2.30 mm) toaccommodate the core biopsy needles), and large vacuum assisted biopsyneedles and their introducer needles (14 to 9 gauge (1.63 mm-2.91 mm),or larger). The ability to infer needle position using signal voidproduced by needle susceptibility artifacts is well established in theprior art, for example, U.S. Pat. Nos. 4,989,608 and 5,154,179 toRatner, U.S. Pat. Nos. 5,744,958 and 5,782,764 to Werne, and U.S. Pat.No. 5,944,023 to Johnson et al.

Delivery of hollow needles for purposes such as acquiring tissue samplesby biopsy, or implanting wires or other markers as guides for surgicalexcision is founded on the same general procedure. Initially the breastof interest is compressed between two plates designed to allow needleaccess to the breast. These plates may take many different forms asindicated in FIG. 8. One embodiment consists of a plate with a largenumber of apertures to guide needles of interest. Other plates contain aseries of apertures of specific shapes and size which provide access tothe breast to prepare for intervention by injecting local anesthesia andmaking a skin incision. These are known as fenestrated plates. An arrayof square apertures have been disclosed in prior art references, forexample, U.S. Pat. No. 5,855,554 to Schneider et al and U.S. Pat. No.6,423,076 to Cardwell et al. Various other implementations may includecircular, triangular, hexagonal, or other aperture shapes, with variouspositioning, or packing orientations on the compression plate 180 asindicated in FIG. 8. Each plate 180 may have features 181 for positionaladjustment (e.g., anterior-posterior). Each fenestration preferably hasan asymmetrical shape to assure proper orientation within the supportassembly 182 that has a membrane 142, fixture for fenestrated plateattachment 183, and fixture for orienting coil attachment 185. There maybe keyed fenestrations 186 and ultrasound transparent membranes 187 inthe assemblies of the compression plates 180. Needle guidance isaccomplished by installing a guide plug with appropriate cross sectionin one of the apertures. These guide plugs have bore-holes sized toguide interventional devices (such as needles) of various gauge sizesand lengths. The simplest implementation involves an array of holes in aplug sized to fit into one of the fenestrated plate's array ofapertures. These smaller holes act to guide the needle into the breastin a straight manner, minimizing the tendency for the needle to deviatefrom a medial-lateral trajectory. Other types of needle guide plugs canbe used with the system. For a particular fenestrated plate, a number ofguide plugs can be provided to accommodate various needle gauge sizes.

The procedure of MRI needle guidance according to the invention isdemonstrated in FIGS. 9 a, b and c. A typical example of such a fixationframe 200 is shown in FIG. 9 a, which serves to hold the breast 220 in afixed geometry during the biopsy procedure and also support MRI-visiblefiducial markers 204, which are used for subsequent registration. Theframe 200 holds the breast while the patient is in a prone position inthe MR system. The frame holds the breast in a medial-lateral direction.The biopsy needle 202 and MR coils 203 are shown. A cancer lump 212 isshown within the breast 220 and guide holes 208 are shown in the guideplate 206. Plug inserts 214 are shown for the window assembly 216. Otherorientations such as cranial-caudal or oblique are possible, howeverhave not been presented in the prior art to our knowledge. A means ofMRI-guided needle delivery as indicated in FIG. 9 has been presented invarious forms in the Prior Art (Orel et al., Radiology, vol. 193, pp.97-102, 1994; Kuhl et al., Radiology, vol. 204, pp. 667-675, 1997;Fischer et al., Radiology, vol. 192, pp. 272-272, 1994; Doler et al.,Radiology, vol. 200, pp. 863-864, 1996; Fischer et al., Radiology, vol.195, pp. 533-538, 1995; Heywang-Kobrunner et al., European Radiology,vol. 9, pp. 1656-1665, 1999; Liney et al, Journal of Magnetic ResonanceImaging, 2000, Su (U.S. Pat. No. 6,163,717), Fischer (U.S. Pat. No.5,913,863), Cardwell (U.S. Pat. No. 6,423,076)) and embodied incommercial breast imaging devices by MRI Devices Inc, USA Instruments,MachTech Inc. The basic premise of this approach is not novel for use asan MRI-guided needle positioning method. This prior art forms the basisof many of the inventions described further in this document whereguidance of needles based on fiducial markers at known relativepositions to fenestrated guides and plates is required. Differingfeatures are highlighted where appropriate with respect to MRI-guidedneedle insertion and the associated apparatus.

Fundamental to MR-guided needle guidance in the manner described aboveis a compression frame constructed of a fenestrated plate 206, whichserves to accept a guide plug 214. As shown in FIG. 9, this holder hasan array of small apertures, on close centers. Fiducial markers 204 areplaced on the grid array of the window assembly 216 and imaged alongwith the breast 220 during the MRI aspect of a procedure. These markers204 are visible in the MRI data set along with the suspicious mass 212.By measuring the location of this mass relative to the fiducial markersin the image, the exact location of the lesion can be determinedrelative to the grid array frame in physical space.

According to the invention, it may be desirable to deliver devices tomultiple locations within the breast (e.g. core biopsy requiringmultiple core samples) or to bring the device along an obliquetrajectory. In these applications, limiting the needle orientation to astraight (medial to lateral) trajectory is undesirable. Positioning theneedle in a straight manner limits the accuracy, which the needle may bepositioned, and multiple samples would require multiple skin incisions.Since device delivery can only be achieved through a finite number ofholes, the specificity of device positioning is limited. So for someapplications a different guide plug capable of defining an angled needletrajectory is required. An embodiment of such a guide plug 230 is shownin FIG. 10. It is composed of a gimbal 240 which allows rotationalfreedom in two directions. The needle guide 232 is a hollow tube passingthrough the centre of the gimbal 240 which allows free rotation of thegimbal 240 about a centre of rotation in the insert form 238. By turningthe clamp 234, it is possible to lock the needle guide orientation. Welater propose a goniometer to set this orientation (FIGS. 11, 12). Sucha design for a gimballed guide plug has been demonstrated in previousU.S. patent documents (U.S. Pat. Nos. 6,195,577 Truwit et al, 6,267,769Truwit, and 6,368,329 Truwit) and is embodied in the Navigus brainbiopsy system developed by Image Guided Neurologics, Inc. However, thedesign of the system of the present invention is substantially differentin that the base of the guide plug can only be positioned in the slotsof the fenestrated plate in one orientation. Furthermore, the presentinvention can be further distinguished from the prior art because theplug is constructed so as to minimize the variations in the needle entrypoint for varying angles of the gimbal as discussed above This isdesired to provide a common entry point to the skin for gatheringmultiple tissue samples. As such, it is desired to have the designoptimized such that the centre of rotation of the needle 233 is close tothe surface of the skin in order to facilitate multiple needle entriesat different needle trajectories without the need to increase the sizeof the incision as discussed above. This can be achieved by removing aportion of the gimbal is shown in FIG. 10 to create a flat zone which isapplied to the skin surface while still providing a spherical surfacefor rotation and locking of the gimbal. In FIG. 10 b, the insert form250 is shown with an alternatively designed gimbal 252.

Once the gimbal is set, its orientation relative to the fenestratedplate must be fixed. This is accomplished by the use of a key or someother unique shape which aligns with a feature in the fenestrations ofthe compression plate. Based on the MRI coordinates, the lesion 260location is defined by two angles shown as α and β, and an insertiondepth z as shown in FIG. 11. The angle β determines the offset angle ofthe needle trajectory 262 from a perpendicular delivery into the tissueand describes a cone with its apex at the center of the needle gimbal264. The surface of the cone passes through the lesion at azimuthalangle α on this cone surface. To prescribe these two angles to the guideplug, a goniometer 270 may be used as shown in FIG. 12. This device is asimple mechanical structure, provides specified orientation of theneedle (not shown) in the gimballed guide plug 272 prior to insertion.The guide plug 272 is placed in the keyed guide plug disc or needleholder disk 274 and a sterile needle guide extender 276 is placed overthe needle guide plug disk 274. This extender is used to deliver thedesired angles in the goniometer system. First the guide plug disc 274is rotated to angle α and the guide plug slider clamp 278 is secured topreserve this angle on the slider ring 280. Then the slider clamp isrotated to define the angle β as shown, after which this is also clampedto prevent further motion. To preserve the orientation of the guideplug, a clamp on the guide plug 234 is activated to lock the gimbal andneedle holder in position. The guide plug can be removed and insertedinto the fenestrated array. Once in position, the needle is advanced thenecessary distance as determined from the MRI data to intersect thelesion as desired.

In order to ensure sterility throughout the procedure, the guide plugdisc, guide plug and needle guide extender can be sterilized for eachpatient, or may be disposable items. If multiple biopsies or entriesinto the tissue are needed, multiple guide plugs can be used, each ofwhich are positioned to the desired location by the goniometer prior toor during the biopsy procedure. With each guide plug pre-set, or setelsewhere by an assistant, the biopsy procedure can be efficient andrapid.

According to the present invention, it is possible to introduce a deviceat an arbitrary orientation while preparing another device orientationin a separate guide plug using a goniometer. The design and use of agoniometer to define and set the position of a guide plug forinterventional procedures is unique with respect to the prior art.Attempts to precisely define angulations through mechanical apparatus atthe site of interest have resulted in bulky and inappropriate devices asdemonstrated in U.S. Pat. No. 6,048,321 by McPherson et al, and aneurological application U.S. Pat. No. 5,984,930, by Maciunas. Specificimplementations for breast biopsy include U.S. Pat. No. 6,423,076,Cardwell et al, and Heywang-Kobrunner 1999. These designs differ in thatthe angular position of the needle is defined by an apparatus attachedto the compression frame immobilizing the breast. In this manner, largebulky apparatus are required and limited angulation is available.

Various embodiments of the fenestrated plates, gimballed plug andgoniometer are possible according to the invention. The apertures of thefenestrated plates, the base of the guide plug and the correspondingaperture in the goniometer are of the same cross-section (e.g.,circular, square, triangular, hexagonal, etc). Furthermore thegoniometer would serve the same purpose if either the arch or the disc(but not both) subtended only one-half of the range shown (i.e. either90 degrees or 180 degrees respectively). In the method of the invention,the needle can be introduced from either the medial or lateral sides ofthe breast by placing a grid plate on the corresponding side of thebreast. The needle trajectory is preferentially determined such that theminimal amount of breast tissue is traversed, however in cases wheremany needle passes may be required, a constraint to minimize the numberof skin incisions and make all passes through one aperture may takeprecedence. This system enables a flexibility to allow for manydifferent needle trajectories to approach the lesion. Similarly, itallows the needle to be introduced at arbitrary angles to ensure safeand appropriate insertion of a needle into a tumour. For example, forlesions near the chest wall, it is imperative that the needle follows apath parallel to the chest wall and not inclined to it, so that thepossibility of chest wall penetration is eliminated.

A weakness with a fixed fenestrated plate is that various regions ofbreast tissue are inaccessible to the needle (areas at the edges of thefenestrated plate and those occluded by the material of the plateitself). Due to limitations on the angulation of the gimballed guideplug, large areas of tissue may be inaccessible. A solution to this isprovided by the present invention as shown in FIG. 13. By decoupling thetwo functions of compression/immobilization of the breast andstereotactic frame, accessibility of the breast tissue can be optimizedto minimize the effects of “blind-spots” in the breast. This fenestratedcompression plate consists of a frame 292 with a sterile plasticmembrane 294 pulled taut across its surface that can be cut andpunctured with a scalpel or a needle (e.g., Opsite™ surgical material,or other membrane transparent to ultrasound). This plate is used tocompress and immobilize the breast. Attached to this frame/membranecombination on the side opposite the breast is a fenestrated plate 290as identified in FIG. 13. This effectively decouples the function of theprevious embodiment of the stereotactic frame: the film compresses thebreast, while the frame provides a plug and needle guidance referenceframe). Fiducial markers 296 may either be attached to the compressionplate 292 or the fenestrated plate 290. The fenestrated plate 290 mustbe designed such that it can be attached to the frame in variousorientations, adjustable for position such that the fenestrations can becentered over different regions of breast tissue. Removing thefenestrated plate and repositioning it into the frame at a differentorientation, or adjusting its position (in superior-inferior oranterior-posterior directions) without removing it would provide accessto tissue which would otherwise be occluded. When the fenestrated plateis moved or removed, the breast would not move relative to thecompression plate, as the function of breast compression andimmobilization is provided by its membrane. Different embodiments ofthis concept are illustrated in FIG. 13. Furthermore, it is important todistinguish that required repositioning of the fenestrated plate toaccess previously inaccessible regions depends on whether fenestrationsare organized in a hexagonally package structure or a rectangular gridand indicated in FIG. 14. For example, in this figure, consider adesired point for biopsy 300. In the various fenestrated plateorientations, the openings have been shifted (by shifting thefenestrated plate within the frame) to assure that the desired targetpoint 300 is accessible through a hole 302. The plates may be shiftedup, down, left and right to align the hole 302 with the target point300. If we had a rectangular grid of holes moving the plate up does notput the point at the centre of a hole. A second repositioning of theplate is required in the S/I direction. As such hexagonal arrangementsare more efficient. As mentioned previously, many fenestrated platesystems are available, and have been presented in the Prior Art. Howevernone have demonstrated the ability to decouple the function ofcompression and providing a stereotactic frame. This invention providesa significant advantage to access the “blind-spots” associated withfenestrated plate stereotactic systems.

According to the invention, both straight and angled needle trajectoriescan be determined with a calculation based on various criteria:

Adopt shortest needle path to target (medial or lateral approach asappropriate, minimal angulation of needle).

Limit multiple samples through a single fenestration.

Select arbitrary fenestration—determine appropriate needle trajectory.

Avoid patient support apparatus and other equipment.

Avoid anatomical features such as chest wall.

Needle Position Verification:

According to the invention, for all MR-guided needle guidancestrategies, MRI verification is required to ensure the needle ispositioned appropriately. However a strategy that includes softwareverification of the needle trajectory before needle insertion can beembodied in the needle trajectory guidance software. Visualization ofthe planned needle trajectory on the MR image set used to identify thelesion can be accomplished by superimposing an indicator on the MRimages. This is particularly important to identify the expected positionof biopsy needles after insertion.

Identification of the lesion after needle insertion may be difficult insituations where the lesion is smaller than the artifact generated inthe MR image. According to the invention, software may be implemented todetermine whether the lesion has moved after needle positioning. Imagingalong the length of the needle (axial image acquisition corresponding toa needle trajectory in the medial/lateral direction), enablesvisualization of the needle depth. Identification of anatomical featuresof the breast before and after needle insertion provides a comparison toidentify whether there has been gross motion of the lesion (inferringlesion motion from the surrounding interfaces when the lesion cannot beidentified). MR images acquired before or after contrast agent injectionprior to needle insertion can be compared to images acquired afterneedle insertion. Scaling and registration of these images, detection oftissue interfaces in the images and determination of the differences inthese edge positions enables measurement of the tissue motion afterneedle insertion. In cases where there is large tissue deflection and/ordeformation, the needle position may be corrected.

EXAMPLES OF CLINICAL APPLICATIONS OF THE INVENTION Example 1 MR-GuidedWire Localization

The use of device guidance techniques to deliver a localization wire ormarker to guide surgical intervention is illustrated in the flowchartshown in FIG. 25. The patient is first positioned on the patient supportapparatus. The breast of interest is then compressed between twofenestrated compression plates with attached fiducial markers, which areattached in turn to the compression plate locking supports. Thesefenestrated plates are sterile and can be introduced while the patientis in the prone position. These plates can be moved in theanterior-posterior direction to positions near the chest wall to enablefull interventional access to the breast. MR imaging coils are attachedto these compression plates. MR imaging is then used to identify thelesion and the fiducial markers. Using this information, the appropriatefenestrated plate aperture and needle guide plug hole are determined inorder to position the needle as closely as possible to the desiredtarget position. Medial or lateral needle trajectories will be selectedto minimize the depth of tissue being traversed, depending on theposition of the target within the breast.

The patient is then removed from the imaging magnet and the marker guideneedle (which is hollow in order to permit delivery of markers throughit) is inserted according to the trajectory calculations. If more accessroom is required, the interventional volume below the breast may beaccessed by retracting the bridge in the transport stretcher. The MRIcoils may be removed as required to provide more access to the breast,and can be repositioned on the compression plates in order to reduce anyinterference with the marker guide needle or wire/marker. The transportstretcher's bridge is replaced. Walls on the side of the stretcher'sbridge may be used to ensure clearance of all devices from the magnetbore. The patient and patient support are next advanced back into themagnet bore and MRI is used to validate the needle position. Strategiesto determine if surrounding tissue has deflected in cases where thelesion may not be well visualized may be implemented based on the imagesacquired. The needle position may be repositioned and again verified forposition. The final step entails insertion of the wire or marker intothe tissue through the hollow guide needle and removal of the needleleaving the wire or marker in place in the breast. The guide plug,fenestrated plate and compression plates may then be removed from thebreast and the interventional procedure completed.

Example 2 MR-Guided Angulated Breast Biopsy

According to the invention, a core biopsy needle may be delivered to thebreast on an oblique trajectory as illustrated in the flowchart shown inFIG. 26. A needle guide plug having straight (medial-lateral) holes of alarger diameter than the biopsy needle, or angulating guide plugs may beused in cases. Patient positioning with fenestrated plates and MRimaging is performed in an identical manner as described under MR-guidedwire localization, with the option of implementing the variouscompression plates indicated in the diagram. Calculation of the needletrajectory is done using compound angles to define the needle trajectoryand a goniometer is used to set the orientation of the guide plug. Incases where access to some targets is limited by the fenestrationaccess, the fenestrated plate's position may be altered without movingthe breast.

Introducer needle insertion is preceded by producing an incision in theskin at the center of the fenestration to facilitate needle entry intothe breast. MR validation of needle position is performed before thebiopsy sample is taken. In cases where small corrections in needleorientation are required, the guide plug gimbal can be unlocked and theneedle orientation corrected by hand. In cases where a large correctionis required, a new needle trajectory can be calculated based on the MRIvalidation images and a new guide plug orientation defined. In caseswhere multiple samples are required, multiple guide plug orientationsmay be defined in parallel with biopsy sample acquisition. Varioussystems in clinical use (Koebrunner 1999, Kuhl 1997) use angulatedneedle trajectories to acquire multiple samples, however this techniqueis unique in that the definition of the guide plug orientation is doneaway from the patient with the use of a goniometer. This enablesmultiple trajectories to be prescribed rapidly and accurately (currentlyin with an included angle of 60 degrees).

Example 3 MR-Guided Marker Placement

The concept of MR-guided biopsy presented in EXAMPLE 2 can easily beextended to placement of small position markers in the breast, accordingto the invention. This may or may not be done in conjunction withMR-guided biopsy, or done in conjunction with MR-guided needlelocalization. This application would take advantage of the fact that alarge tissue segment can be accessed through a single incision point(repositioning of the fenestrated plate to provide better access may berequired). As shown in FIG. 15, a linear tumor 320 can be delineated byway of a set of markers 326 These markers 326 may be identified afterthe procedure defining the maximal extent of the tumor. Markers such asendovascular occlusion coils, surgical clips, or any of the devices asdisclosed by Foester et al. in U.S. Patent Application Ser. 2002/0193815A1 may be used. Furthermore, radiotherapy implantable seeds, or localchemotherapy delivery devices may also be distributed around theperiphery of the tumor. Clips can be delivered through the center of ahollow needle 324, and when fully extended and uncoiled, they remainfixed in the tissue at the end of the needle 324. These clips would haveto be made of the appropriate MR-compatible material (e.g., titanium,platinum, stainless steel, etc.) to ensure they can be identified and donot compromise subsequent MR images, and to ensure they can be safelyused within the MR magnet room. The use of this procedure according tothe invention is illustrated in the flow chart shown in FIG. 27.

Example 4 MR-Guided Interstitial Therapy Delivery and Monitoring

In the method of the present invention, the techniques described abovemay be easily extended to deliver a variety of tissue investigation orablation devices such as invasive ultrasound tissue ablation devices,RF-heating devices, cryotherapy systems, local delivery ofchemotherapeutic agents, local delivery of radioactive material fortherapy, optical ablation (lasers), optical photodynamic systems or anyother tissue destruction technique. Monitoring of these devices may bedone using MR imaging to measure temperature distributions, chemicalconcentrations or other parameters during therapy. In the case of theoptical systems, the treatment region may be defined using othertechniques (i.e. T2-weighted contrast sequences).

MR/US Hybrid Imaging and Intervention

With the system outlined above, an apparatus for delivering a device toa lesion is described with an arbitrary trajectory. However, the needlepath may deviate from the planned trajectory due to either tissueheterogeneity which can cause needle deflection. A hard lesion andsurrounding tissue may move during device entry. Further, the ability tobiopsy small lesions can be limited due to the size needle-generatedartifact on the MR images as previously mentioned. This is particularlyproblematic when preformed on a high field imaging system (i.e., greaterthan 1.5 T magnetic field strength). Ideally, a means to observe theneedle path in real-time is optimal to ensure correct lesionpenetration. According to the present invention, an ultrasound imagingcapability can be added in the same biopsy apparatus in order to delivera US transducer using the same stereotactic delivery strategy asoutlined in the previous section. A device can then be delivered intothe breast under the guidance of this real-time US imaging in severalways.

Through a simple modification to the biopsy system, removal of thecompression plates and substitution with an acoustically transparentwindow held in a frame containing fiducial reference points, theinvention can be used to perform hybrid (MR/US) imaging. This aspect ofthe invention involves detecting the lesion using MRI, than removing thepatient from the MR magnet's intense field to perform US imaging. Usingthe system in this manner constitutes an automated strategy to identifyMR-detected lesions in US images as well as a means of fusing MR and USimages. The real-time US data can be used to position a deviceaccurately into the lesion and to verify its position. This may be doneusing US exclusively when the lesion can be identified on the US image,or using a combination of the MRI and US data if the lesion is noteasily identified using US, or if the patient may have moved.

The approach to breast imaging disclosed by the present invention hasmany useful clinical applications as generally demonstrated in thefollowing examples. These applications can also be extended to existingMR and US imaging modalities (e.g. contrast-enhanced MRI/US, compound USimaging, US Doppler imaging, etc), or to those available in the future,without departing from the scope of the invention.

Example 5 Hybrid MRI/US Imaging

This application involves accurate location and assessment of extent ofan MRI-detected lesion using US in the same procedure while the patientremains in the same apparatus that was used for MR imaging. This offersan alternative to retrospective US detection of MRI-detected lesions intwo different procedures. This retrospective technique can be inaccurateand time consuming as the patient is in two very differentconfigurations for both imaging procedures. This relies on the skill ofthe radiologist to mentally transform data from the two modalities.Hybrid MR/US imaging enables the radiologist to confidently identifyMR-detected lesions using US which may allow them to improve diagnosticability based on features visible under US. It also allows them toidentify anatomical landmarks which can be used for subsequent US-guidedbiopsy with the patient removed from the biopsy apparatus. Knowledge ofthe US characteristics of the lesion could lead to easy identificationof the lesion in a follow-up US examination. In cases where the lesionis difficult to identify on the US image, the option to view the lesionas an image where MR and US-visible features are combined.

Example 6 Hybrid Biopsy

This application of hybrid imaging involves biopsy acquisition underUS-guidance while the patient remains on the biopsy table with theirbreast immobilized. The region of interest for US examination isidentified using previously acquired MR images. This procedure involvesstereotactic delivery of the US transducer in conjunction withfree-hand, or stereotactic delivery of the biopsy needle. This may beaugmented by the use of combined MR/US data set, and with or without theuse of a US transducer whose position and orientation are measured inreal-time, and/or tracked biopsy needle. This image can be superimposedonto the MR/US fused dataset in such a way that the needle is easilyidentified on the MR/US fused image set, and in a way that the presentedMR/US image(s) updates with the changing position of the US transducer.

Example 7 Hybrid-Guided Marker Placement

In a similar manner as hybrid-guided biopsy, and in the same way asMR-guided marker placement differed from MR-guided biopsy, this systemcan be utilized to place numerous implantable devices to denote breasttumor extent. In this case the applicator needle placement will beperformed using US-guidance and may be done either using free-handapplicator guidance or stereotactic needle delivery with the ability tocorrect for applicator and tissue deflection. In this case the fusedMRI/US data may provide better determination of lesion boundaries thanUS guidance would give alone.

Example 8 Interstitial Therapy Device Delivery and Monitoring

The hybrid device delivery technique may also be used to deliver devicesother than biopsy needles, or marker placement devices. This system canalso be used to position a variety of tissue investigation or ablationdevices, such as invasive ultrasound tissue ablation devices, RF-heatingdevices, cryoablative systems and, optical photodynamic systems asdescribed previously. In many cases it is advantageous to monitor thetherapy using the US images, particularly using cryotherapy. Thistechnique may offer the ability to improve the accuracy of the delivery,was well as reducing the amount of MR imaging required. Again this canbe done using the combined MR/US data set, or using only the US data ifthe lesion can be confidently identified on the US image. However, theuse of the combined MR/US data may be beneficial as MRI may provide muchbetter definition of tumor boundaries.

In all applications described above, US imaging modes (e.g. Doppler, 3Dimaging, US contrast agents) may improve lesion detection. According tothe invention, various means of image fusion can be used to assist inimage correction in both the MR and US images.

For all MR/US hybrid imaging procedures set forth in Examples 5-8,standard apparatus may be used as outlined in the following section. Themethods are useful for accurate location of the US transducer to allregions of breast tissue, transformation of coordinates between the MRand US imaging data, MR/US image fusion/integration techniques, MR/USimage correction and reformatting. According to the invention, thisequipment can be integrated with the biopsy system presented in theprevious sections, (i.e. the patient support, biopsy table, compressionsystem, MR imaging coils).

US Transducer Delivery

Another aspect of the invention provides the ability to deliver an USimaging transducer to a particular MR-detected position in space usingMR-detectable fiducial references. A US transducer holder andpositioning apparatus is affixed at a known position relative to thesemarkers. If the position of a target on an MR image is known relative tothese MR detected markers, then the position of a US transducer relativeto these same markers can be calculated such that the device and thecorresponding US imaging plane can intercept that target. If the USimaging plane and field of view is known relative to the US transducer,then a transformation from MR to US image coordinates can be obtained.The devices involved include a constraint plate incorporating anacoustically permeable membrane to immobilize the breast, a stereotacticframe with embedded/attached fiducial markings 340 and attachment points344 for a transducer positioning/tracking system 342. FIG. 16, FIG. 17,FIG. 18, and FIG. 18 a show these components. FIG. 16 is the positioningstage where a mechanical stage with five degrees of freedom and capableof two different transducer orientations allows accurate transducerpositioning. FIG. 17 is the tracking system with a free-hand positiontracking device 350 and registration apparatus for free-hand tracking352. FIG. 18 shows how a nest 360 may be positioned in two or moreorientations. FIG. 18 a shows touch points 370 at known positionsrelative to MRI visible fiducial markers to provide an alternative meansof free-hand registration.

In the method of the invention, the function of the membrane is toprovide a means to compress the breast as well as provide a window forUS imaging. A polymeric membrane that is acoustically matched and isthin enough to not attenuate the US beam in a manner that affects USimage quality is suitable (e.g., polyethylene, polystyrene, polyester,polycarbonate, etc.). It is important that the breast is well compressedand that the breast is coupled to the membrane (US coupling gel isapplied between the breast and the membrane before the procedurebegins). Designing the membrane such that it bends a small amount toconform to the curvature of the breast ensures that there is maximumcoupling between the breast and the membrane. This allows maximumimaging access to the breast (FIG. 19 a, b, c, d). Strategies toconstrain the breast in other directions enable full access to all ofthe breast, including regions behind the nipple. In an initialpresentation of this concept devoid of technical details, theanticipated implementation involved US imaging and interventionoccurring on opposite sides of the breast (Plewes et al, 2001 IEEEUltrasonics Symposium). This was the only presentation of this conceptas Prior Art. However this simplistic embodiment without redesignedpatient support for probe and needle angulation capacity and without acompression membrane and breast constraints in other orientations provedto be ineffective for clinical usage. The compression membraneconfiguration presented in FIG. 19 is key to providing complete accessto the breast, and at first glance is not obvious. FIG. 19 a, 19 c showthat lesion 402 is difficult to access with ultrasound (US) imaging witha taut frame holding the membrane 400 stiff. FIG. 19 b and FIG. 19 dshows compression with a larger, deformable membrane 404 that placesmore membrane in contact with the breast. In FIG. 19 a and FIG. 19 c,the two rigid frames 406 also make the breast difficult to access for USimaging, while in FIG. 19 b, 19 d the curvature 408 (as seen from belowthe breast) allowed with a less rigid or taut system allows the lesions410 more accessibility in US imaging.

According to the invention, the US transducer holding and positioningsystem can take two general forms; 1) a mechanical stage, 2) a free-handtracking device. Both techniques involve holding an US transducer in aconformal nest which is then attached to either a mechanical stage, orto a tracking device at a known position and orientation. A mechanicalpositioning system enables accurate positioning of the transducer withvarious degrees of freedom. This positioning system is then attached tothe compression plate at a known position with the axes of USH motioncorresponding to the MR imaging axes (L/R, A/P, S/I), and therefore tothe physical frame of reference. This facilitates transformationsbetween the MR frame of reference and the transducer frame of referenceas well as eliminating the need to register the positioning apparatus tothe stereotactic frame during the procedure. In the embodiment shown inFIG. 18 the transducer can be moved through 5 or more degrees offreedom. This design, with positioning tracks on the periphery of thebreast imaging volume, enables access to areas near the chest wall,which is critical for complete access to the breast. The rotational axesof the positioning system further enable the transducer to be angled toimage regions of breast tissue that would be inaccessible with a simplehorizontal or vertical imaging approach. The design of this stage allowsfor large angulations of the transducer without interference. Thisdevice ensures that the transducer can be moved in the vertical (A/P)and horizontal directions (S/I) with the transducer face always incontact with the membrane surface. This allows for effective scanningthrough the breast volume, facilitating 3D US imaging applications andalso enables a lesion to be inspected using multiple transducerorientations. This design further enables accommodation of varioustransducers during the procedure by interchanging the transducer nest.The position of the US imaging plane is known because the position ofthe transducer relative to the USH is known. The ability to easilyremove US transducers from the USH allows the radiologist position theUS transducer by hand. Once a lesion is identified in the US image, theUS transducer can be removed from the nest and be manipulated free-hand.This allows visualization of the lesion through multiple imaging planeswhich is known to be a critical element of US imaging, however onceremoved from the nest, the position of the transducer is no longerknown. There are no inventions presented in the Prior Art that pertainto a mechanical positioning stage for an US transducer accounting forthe presented constraints.

The invention also provides another tracking option that more closelyresembles the traditional manner of imaging with the US transducer;namely, a 6 degree of freedom tracking device (or other lower orderdegree of freedom systems) such as an optical (fiber optic),electro-magnetic tracking, ultrasonic tracking, or other non-contactposition tracking system in which the transducer is free to move inspace without fixtures. This aspect of the invention accommodates atechnique which is more familiar to the radiologist; however, theaccuracy with which the transducer can be free-hand positioned to aparticular position may be limited. To use such a non-contact trackingsystem to determine transducer position relative to the fiducialmarkers, the orientation of the tracking system must be calibrated tothe orientation of the stereotactic frame, and thereby to the MR imagecoordinates. This can be accomplished by positioning thetransducer/receiver at points on the stereotactic frame at knownpositions relative to the fiducial markers, measuring these positionsand determining a correlation to convert the tracking system coordinatesto the corresponding MR coordinates and vice versa.

In another embodiment of the invention, an algorithm is applied whichtranslates a given MR-detected coordinate to a corresponding USHposition for a given US transducer in a given orientation (vertical orhorizontal for the USH system presented in FIGS. 16, 17, 18 and 18 a),such that the target of interest will appear in the center of thetransducer imaging field at a calculated depth. A US imaging plane canbe identified such that the shortest imaging distance to the lesion isselected, or to intersect the lesion using a specific transducerorientation. This algorithm enables conversion of a single MR-detectedposition to a set of USH axis-positions and a unique position on the USimage. Techniques to register and fuse MR and US images (i.e. more thanone corresponding point at one time) are explained in the followingsection.

Image Integration:

The present invention provides a method for registering MRI and USbreast images (2D and 3D images) to various levels of sophisticationbased on accurate stereotactic transducer positioning and/or subsequenttransducer position tracking. By knowing the orientation of the UStransducer, a 3D MR data set can be reformatted to generate an MR imagethat corresponds to what is visualized on the US image (i.e. generate a2D image from the 3D MR image set that is the same scale and size andcorresponds to the same plane as the acquired US image). The actualtransducer position can be determined by either the mechanical systems,or the non-contact transducer position measurement systems presentedpreviously. Presenting the two images side-by-side allows theradiologist to validate that the lesion and surrounding structures inthe US image correspond with the MRI data. Segmentation (imageprocessing) and integration of the MRI data in ways to depict anatomicallandmarks and functional information such as contrast agent uptakeparameters would facilitate identification of the lesion and surroundinglandmarks in the breast. This system can further be enhanced bynon-contact position tracking of devices such as biopsy needles, ortissue ablation devices. Tracking the position of devices permitsindication of the device position on this reformatted MR data andpermits free-hand device delivery without guidance plugs or fenestratedplates. In addition, the real-time position-tracked US image of a devicecan be superimposed onto this image.

There are many tracking systems in the Prior Art related to the trackingof devices for the purpose of display and manipulation of medicalimages. In Comeau et al, (Med Phys, 27(4), 2000) a presentation of suchan integrated system for the purpose of tracking an US probe relative toa patient's skull for the purpose of co-registration with respect to aset of pre-acquired MR images was presented. Here a method of opticallytracking the US probe, and using US information to help correct fortissue shift errors associated with MR brain surgery was presented. Theuse of such a system to assist brain surgery is facilitated by theconstraining nature of the boney skull. Such a concept has not beentranslated to deformable structures such as the breast as there has beenno way to appropriately constrain the breast while providing adequateaccess required for intervention. Furthermore, the proceduraldifficulties associated with previous attempts have precluded itsfurther development. An integrated system as presented in the inventionenables application of image co-registration techniques in a way that isclinically practical.

Similarly, according to the invention, MR data can be displayed with asuperimposed marker indicating the position of the scan plane of the UStransducer. Visualization strategies such as maximum intensityprojection could be used to effectively depict the 3-D MR data in a waythe radiologist can clearly interpret. Furthermore, four-dimensional, ortime series data could be combined and presented as a 3 dimensionalcolor-coded representation. This technique would be most useful when afree-hand tracking system is used for the transducer.

In the method of the invention, the same concept of image registrationand image integration could be extended to modify the real-time USimages. Segmenting the critical structures from the 3D MR data (i.e.anatomical landmarks, contrast-enhanced lesion), and knowing theposition of the transducer relative to the MR data by way of a trackingsystem, the two image modalities could be integrated into one image.This technique does not require the lesion to appear in the US image.Rather the MR image of the lesion is identified as the target and issuperimposed on the US image. The radiologist could simply adjust thetransducer until the superimposed lesion appears in the US image, andguide a needle to that point at a trajectory determined using knowledgeof the transducer position. Similarly, the image may include asuperimposed marker representing a position-tracked device to assist inits visualization. Image fusion in this manner will also permit aquantitative measure of the accuracy with which the images have beencombined. A measure of how well the MR and US modalities are registeredcan be obtained by performing a cross correlation calculation at anytime. The radiologist can ensure that the registration is accuratebefore proceeding with the intervention. In the method of the invention,the integration of 3-D MRI and 2-D US information and the overlay ofsegmented data (data which has been processed to highlight anatomicalfeatures), needle position and US image plane orientation enablesreal-time tracking of the needle position and US beam path to facilitatereal-time guidance of a device towards a target by ensuring they areco-aligned throughout the imaging/intervention procedure.

There is no known Prior Art presenting a system that incorporates thesetechnologies so as to provide an MRI/US combined approach to performintervention, or imaging procedures on MRI detected targets in non-rigidregions of the body that are required to be constrained to reduce errorsassociated with motion and deformations. The physical and mechanicalrestrictions associated with such an invention have been presented asaspects of the invention thus far.

Image Error Correction:

The present invention also provides for integration of MR and US data,whereby information from one modality can be used to correct errorsassociated with the other modality.

Correction for US Positional Errors

Another aspect of the invention provides image integration techniques,whereby MRI data can be used to correct for errors in the US data set.It is well known that the location of features in a US image isdetermined using known values for the average speed of sound in tissue.However, fat and fibrous tissues are known to exhibit speeds of soundthat differ by 5-10%. In routine US images, a fixed speed of sound isassumed to determine location. This is an approximation and will resultin positional errors in the co-registration of the MR and US data sets.For example, if the space between the skin surface and the lesion iscomposed of purely fat and represents a thickness of 3 cm, then thelocation of the lesion in the US image would be in error byapproximately 1.5-3 mm and as such the MRI and US images would not beaccurately co-registered. In most applications of US imaging, this isnot a limitation, as relative position is often all that is required. Inthe method of this invention, absolute position in terms of an MRIcoordinate frame is what is required. In practical terms, the maineffect of the assumption of constant US speed-of-sound will be todistort the image in the direction parallel to the sound propagation,causing the image to be either compressed or expanded depending on theassumed speed of sound. However, refraction together with the fact thateach point in the image is formed by multiple RF measurements from eachelement in a typical US transducer can lead to lateral distortions aswell. This will be evident on the US image as spatial errors or regionsof misalignment as one attempts to overlay the US and MRI image. Inorder to overcome these distortions corrections for the actualspeed-of-sound for each transducer element must be made reflecting theactual tissues through which the US field propagates. Two possibleapproaches can be taken to overcome this limitation.

An approach is to attempt to correct for speed of sound variations bycombining the MRI and US data. This can be achieved in an interactivefashion by repeatedly correcting the US data on the basis of knowledgeof the tissue composition from the MRI data. In its most simple form,the MRI data can be used to make a first order correction of US positionby estimating the amount of fat and fibroglandular tissue through whicheach US measurement is made. We note that standard T1-weighted MRIimages render fat and fibroglandular tissues with very different signalintensities. Typically, fat appears with a high signal level (bright) asa result of a short spin-lattice (T1) time constant while fibroglandulartissues with longer T1 times, exhibit a lower signal and are seen as adark region on the image. One this basis of this contrast between thesetwo tissues, it is straightforward to segment the varying regions of theMRI data from which to calculate the distant of US propagation (andspeed) for both fat and fibroglandular tissue. As the location of the UStransducer has been positioned over the tissue on the basis ofmeasurements from the MRI image, we know the position of the UStransducer in the MRI imaging field to first order. From this thecorresponding paths of the US field for each US transducer element canthen be determined for each point within the US image. By referring tothe same point on the MRI data the path length of the fat andfibroglandular tissue can then be estimated and the corresponding speedof sound variations for that location and US transducer element can bedetermined. This can then be used to scale the all the US RF data to thevarying speed of sound within the tissue. The corrected RF data can thenbe combined to form the US image and create a corrected US image. Thiscorrected image will represent a first order correction to align the USand MRI data. When attempting to overlay the US and MRI images, theboundaries of well-defined anatomical structures, such as interfacesbetween fat and fibroglandular tissue, should be better coregistered.

As a result of this operation, each point in the corrected US image willnow be closer to its true location within the US image. This sameprocess could be repeated in an interactive or interactive manner witheach successive iteration moving the points in the US image to graduallymigrate to their true corresponding location on the MRI data.

The discussion above, presumes that the geometry of MRI data isgeometrically accurate; however, it is known that various factors willmake the MRI image also exhibit spatial distortions. The mostsignificant of these are positional errors arising from magnetic fieldgradient non-linearities. Most manufacturers of MRI equipment attempt toprovide some form of correction for these gradient non-linearities onthe basis of pre-determined measurements of the gradient spatialperformance over the 3D imaging volume. In order for the segmentationscheme outlined above to be most effective, correction of MRI data isneeded.

An alternative approach to this problem is to use image co-registrationmethods to map the US data to the MRI data. A number of co-registrationmethods exist which transform the location of point with one image tobest match its location in another by satisfy varying metrics of imagesimilarity such as mutual information (Hill D L, Batchelor P G, HoldenM, Hawkes D J Medical image registration Phys Med Biol. 2001 March;46(3):R1-45.). With these techniques it would be possible to correct forsubtle changes arising from variations in the speed of sound in the USimages and match them to MRI images. As such, lesions which are expectedto appear on the US images can be determined uniquely from MR image. Inaddition, we could use the calculated deformation field to calculate thespeed of sound variations that would be needed to generate thisdeformation in an iterative manner similar to that described above. Assuch, the MRI data will be used to constantly update the US data inreal-time to provide accurate co-registration of the two data sets.

Defining the MR Image Plane to Track US Transducer Motions

A further aspect of this invention uses motions detected with US dataduring an intervention to modify the MR image, reflecting the new tissuegeometry. The MRI image would appear to be updated in a real-timemanner, without necessitating acquisition of new images in the MRmagnet. In the method of the invention, the entire post-MRI imagingoperation could be done outside of the magnet room by detaching thetransport stretcher from the magnet and rolling the patient out of themagnet's field. This would reduce the amount of time needed for MRmagnet access but ensure that meaningful use of the MR images would bemade during an intervention. Further embodiments include gathering 3D USdata (rather than the normal 2D images) during intervention to monitortissue and device motions. Another embodiment involves measuring theorientation of the needle from an external tracking system to overlaythis estimate of device orientation on the image data. This would serveto corroborate the device orientation with that visible on the US image,helpful when the device position is unclear in the US image.Furthermore, US imaging serves to reduce the need for further MRI.

As mentioned previously, Cormeau et al, 2000, presented a system thatintegrates US and MRI data registered using fiducial points and withprobes positioned and tracked using an optical tracking system. Thisembodiment has been specifically developed for brain applications anddoes not translate to breast applications for reasons previouslymentioned. Tissue shift correction techniques presented by Cormeau usinginformation from both modalities can be translated to the breastapplication. The current invention differs in that a well-immobilizedbreast with US imaging access provided through multiple access points(medial and lateral) enables high quality US imaging (shortest distanceimaging to the target) to be performed without gross tissue motionassociated with craniotomy associated with neurological procedures. Thecurrent invention also considers the nature of imaging errors associatedwith mis-registration errors not considered by Cormeau.

ADDITIONAL EXAMPLES OF CLINICAL APPLICATIONS OF THE INVENTION Example 9Hybrid MR/US Imaging

The simplest implementation of hybrid imaging involves the detection ofa lesion using MRI, followed by positioning of an US transducer, suchthat the lesion appears in the center of the US field of view at acalculated position, as illustrated in the flowchart shown in FIG. 28.

The breast of interest would be compressed between two acousticallytransparent compression plates. Attached to these compression plateswould be an array of coils for MR imaging. The lesion would be detectedusing MR imaging techniques and other MR imaging techniques may be usedto identify features of the breast that would be visible using US. Thiswould serve to provide features common to both imaging modalities (e.g.T2-weighted MR imaging is appropriate for imaging cysts, T1-weighted forfat-fibroglandular interfaces). The position of the target lesion andthe fiducial markers as seen on the MR image would be entered into acomputer program which determines the appropriate USH co-ordinates suchthat the lesion will appear in the US image. The ability to image frommedial or lateral sides of the breast without prior knowledge of thelesion position ensures optimal images may be obtained from the sideclosest to the lesion. After finding the lesion under MRI, the patientis transported from the MR imaging system while still immobilized on thepatient stretcher, away from the magnet's field. At this point the MRimager is free to be used for another patient. The MR imaging coils arethen removed from the compression plates and the mechanical, or freehandUS position tracking system may be attached. The transducer can thenaligned with the lesion as indicated by the MR image. The lesion ofinterest should appear at the center of the US image, at a calculateddepth from the surface of the imaging face. Lesions can then be freelyexamined using a variety of US techniques.

In some cases, the lesion may be difficult to visualize in the US image,or the position prescribed for the US transducer may be in error forvarious reasons. In these cases, additional techniques can be appliedwith some increase of complexity. The techniques of MR/US imagefusion/integration and image correction may provide the radiologist withtools to aid in identifying the lesion and provide more accurateregistration between the images. Freehand transducer positioningprovides a means of visualizing the lesion in three dimensions byimaging it through different planes. One important technique involvesthe identification of common features found in MR and US images in orderto confidently identify the lesion.

In FIGS. 20 and 21, various MR/US Hybrid biopsy configurations areshown. In a lateral biopsy approach in FIGS. 20 a, b, c and d, a breast458 (for example) is compressed between two sterile, US permeable plates451. Imaging and intervention occur from the same side. FIGS. 21 a, b, cand d are essentially the same configuration as FIG. 20, with a medialbiopsy approach selected. FIG. 20 b is a configuration with onefenestrated plate and one US permeable plate. Needle approach is fromthe opposite side from US imaging. FIG. 21 b is the same configurationas FIG. 20 b with a needle guide plug used to deliver needle. FIG. 20 cuses a plate with larger fenestrations which can be used to incorporatea transducer and needle for same side imaging and intervention. FIG. 21c is the same configuration as FIG. 20 c showing a view from a lateralside. FIG. 20 d shows an alternative transducer and needle deliverythrough the same side using a positioning stage. FIG. 21 d is anotherembodiment with 2-point needle positioning system on opposite side to USimaging.

A radiologist may use the information in the registered MR/US images todetermine the pathological status of the tissue in question. Forexample, a breast lesion may be defined as malignant or benign based onwell-understood features visible in the US image such as lesionmorphology, or blood flow characteristics. The radiologist may alsoidentify unique features of the lesion such as its appearance, size orlocation relative to anatomical landmarks in order that it may beidentified on a subsequent retrospective US-guided biopsy.

Example 10 Hybrid Biopsy

A preferred embodiment of the hybrid imaging technique disclosed by thepresent invention is its application in acquiring biopsy samples oflesions that are detected using MRI and cannot be biopsiedretrospectively through any other traditional means (e.g. if the lesionis not identifiable on the basis of US alone). Biopsy would then beperformed making use of hybrid imaging.

According to this invention, the procedure for hybrid biopsy is similarto that for hybrid imaging, but in addition a biopsy needle would beintroduced into the breast with US verification imaging. The generalprocedure is illustrated in the flowchart shown in FIG. 29.

This procedure requires the same apparatus as the hybrid imagingprocedure, except the compression plates used would differ and a needleguidance strategy and apparatus may be incorporated into the procedureas required. Various setups for the procedure are shown in FIG. 21 andFIG. 22. In all cases shown, the contralateral breast is compressedagainst the chest wall. However both breasts can be constrained betweenplates and biopsied if both breasts extend into the interventionalvolume below the patient support. This would limit the biopsy approachto a lateral approach on either breast.

In each of the configurations shown in FIGS. 20 and 21 a, b, c and d,the compression plates have electrical connections for MR imaging coils(connections not shown). MR imaging is performed to detect the tumor andbreast's features along with fiducial markers. The relative positionsfiducial marker and target lesion are used to determine appropriate USHaxis positions, bringing the US imaging plane through the lesion. Afterthis point the biopsy techniques employed differ according to theparticular strategy used.

According to one aspect of the invention, the breast of interest wouldbe compressed between two US-transparent compression plates, as shown inFIGS. 20 and 21 a, b, c and d. These plates would be prepared with asterilized membrane, as well as requiring that the coupling gel betweenthe membrane and the sterilized breast would be sterile. Such acompression system presented as a sterile surface and an acousticallytransparent member has not been presented in any Prior Art and isfundamental to the success of such a technique. After lesion detection,an appropriate US transducer position would be determined such that thefollowing criteria are satisfied: i) the shortest imaging distance isselected (either medial or lateral approach) ii) transducer positionprovides clearance for biopsy needle entry and avoidance of biopsysystem components, iii) the transducer orientation is optimized forlesion visualization. The transducer may be delivered to the appropriateorientation using the USH device and/or a free-hand tracking technique.The transducer positioning technique that provides the greatest accessto the breast for needle positioning is preferred. The access providedby the system to the breast further enables the option of freehand USimaging with one hand from one side of the breast, and needlepositioning from the other side of the breast. This configuration maynot be optimal from the standpoint of the radiologist's dexterity,however this approach option is provided in one embodiment of theinvention. The approach shown in FIGS. 20 and 21 with needle deliveryand US imaging from the lateral approach would be used when the lesionis positioned in the lateral region of the breast. The approach shownwith needle delivery and US imaging from the medial side of the breastwould be used when the lesion is located in the medial region. In allcases the lesion would first be identified on the US images using thetechniques previously presented. When identified, the transducer wouldbe positioned so as to provide room for needle entry, or positioned soas to monitor the needle as it is introduced into the breast. In caseswhere the lesion is not obvious, addition of MR/US fusion strategiescould be applied. Further application of needle tracking andpresentation on the fused image set would also be of great benefit inthis application as well as all other hybrid imaging strategies toassist in needle identification.

In another embodiment of the invention, the breast would be compressedbetween one US-transparent compression plate and one fenestrated plateon the opposite side, as illustrated in FIGS. 20 and 21. It is customaryto select the shortest biopsy trajectory in order to minimize breasttrauma. In this configuration the hybrid biopsy concept can be performedin a variety of ways, each using the basic concept of US transducerpositioning and either free-hand needle delivery or stereotactic needledelivery. These techniques are described below, in accordance with theinvention.

1) Stereotactic US Transducer Delivery, Freehand Needle Delivery

The lesion and fiducial are located using MRI. The patient/biopsyapparatus are removed from the MR imager and apparatus prepared for USimaging and needle intervention. The US transducer would be deliveredaccording to MR image coordinates, and the lesion is identified on theUS images. The US transducer may be repositioned to aid in identifyingthe lesion. On the opposite side of the breast, the appropriate apertureof the fenestrated plate is selected for needle entry using knowledge ofthe lesion's position. The needle would be introduced into the breastand its trajectory modified based on the US images. A biopsy samplewould then be acquired the guide needle is in the appropriate position.Multiple samples may be acquired using, offsetting the biopsy needle'sposition for each. Multiple lesions may also be examined in the samebreast, in the same procedure using this strategy.

2) Stereotactic US Transducer Delivery, Stereotactic Needle Delivery (NoMR Verification)

This embodiment of the invention is similar to the one proposed above,differing only in the extent to which the MRI data is used to helpposition the needle and transducer. The lesion and fiducial markerswould be identified using MRI. These positions would then be enteredinto a program that would determine the appropriate needle deliverytrajectory based on the shortest distance to the lesion, or restrictedto a fenestration selected by the radiologist. Based on the needleorientation, the transducer orientation would be calculated such thatthe needle would appear in the plane of the US transducer as it isintroduced into the breast. The patient would then be removed from themagnet bore, and prepared for US imaging. The US transducer would bepositioned according to the above calculation and the lesion identifiedon the US image. The needle would be introduced into the opposite sideof the breast through the needle guide plug and its trajectory modifiedbased on the MR or US verification images. The guide plug may beloosened and the needle trajectory modified as required. Multiplesamples may be acquired.

3) Stereotactic US Transducer Positioning, Stereotactic Needle Delivery(MR Verification)

In a third embodiment of the invention used with this plateconfiguration, MRI is used to detect and to validate the needle positionbefore the US imaging procedure is performed. The lesion and fiducialmarkers would be located using MRI. The appropriate needle deliveryorientation to the lesion would be calculated based on the MR data suchthat the shortest distance to the lesion would be selected (alsoconsidering the positioning of the US transducer and limitations of theapparatus in the immediate area). An MRI compatible needle would then bedelivered to the lesion at the desired orientation using the angledneedle guide plug presented previously. MR imaging would then be used tovalidate needle position. The needle position may be modified asrequired with additional MR imaging. The patient would be removed fromthe MR magnet room and the apparatus setup for US imaging. The UStransducer would be positioned to an appropriate orientation to allowthe needle and lesion to be imaged. The needle trajectory may bemodified as required by unlocking the needle guide plug before thebiopsy sample is acquired.

The examples presented above are all embodiments of the invention. Eachembodiment has certain advantages. For instance, one embodiment requiresthe operator to deliver the needle by free-hand guidance. This strategyis a fast technique requiring no needle guidance apparatus, however itrelies on the radiologist's dexterity. A second embodiment (employingstereotactic needle delivery outside the MR magnet) requires moreapparatus; however it provides a fast means of needle delivery and hasfewer demands for accuracy on the radiologist. The third embodiment,which requires MR-verification of the needle before US imaging/needleverification is a longer procedure, however it does provide anadditional MR image as verification. The last embodiment is limited inthat the patient must remain in the prone position with the biopsyneedle in the breast for a longer period of time.

In another aspect of the invention, fenestrated plates that haveopenings large enough to accept either the front end of an UStransducer, or a biopsy needle, or a needle guide plug, are positionedas medial and lateral compression plates. This configuration enablesimaging and intervention from either medial or lateral approaches. Thisconfiguration further enables free-hand biopsy, or stereotactic needledelivery techniques. The design of the plates should be such that theopenings are large enough to allow the transducer access to the breast,however not large enough that a large volume of breast tissue bulgesthrough the openings. According to the invention, an acousticallypermeable membrane is pulled taut and positioned between the breast andthe fenestrated plate can be used to constrain the breast in thisimplementation. This has the benefit of good breast immobilization, goodaccess for US imaging, and provides a frame to which needle positioningplugs may be attached.

In yet another aspect of the invention, two different needle positioningstrategies are applied. The implementation of the two-point needlepositioning device corresponding to the US transparent membrane is shownin FIGS. 20 d and 21 d. This can be used on either the same side of thebreast as the US transducer or, as shown here, on the opposite side. InFIG. 21 d we see an additional needle guide attached to the UStransducer positioning device.

In all of the above hybrid biopsy strategies, the lesion may not bevisible to US. In some cases the lesion may not be identifiable due topoor US image contrast. In these cases, the operator may choose tobiopsy the tissue identified by the MR images. A biopsy may be acquiredmore confidently if image fusion techniques are employed. According tothe invention, other imaging techniques, including US Doppler, Harmonicand US micro-bubble contrast, may be used to enhance the quality of theimages acquired. In the method of the invention, all biopsy strategiescan be extended to multiple lesions in a single procedure. None of thesetechniques have been described in detail in previous Prior Art. Anarticle by Plewes 2001, IEEE, presents a simplistic form of thetechnique where US and needle delivery is performed from opposing sideswith the shortest distance taken to be from the needle insertion tolesion center, however none of the enabling aspects of the inventionwere presented.

Example 11 Hybrid Marker Placement

According to the invention, using a technique similar to MR-guidedbiopsy of the breast, a small position-marking device may be implantedin the breast in conjunction with a biopsy or wire localizationprocedure. Any of the previously presented hybrid biopsy techniquescould be applied as needed. Marker placement using MR-guidance alonewould require multiple image acquisitions to verify position prior toeach marker placement. Lesions only visible under contrast enhancementcannot be imaged repeatedly with MRI during the same procedure. Guidanceof marker placement devices using US is not restricted by time-limitedlesion contrast enhancement, and does not require long periods ofexpensive MR magnet time. US cannot always be relied upon to visualize alesion's exact location or extent, but can be used to track tissuemotions during the intervention. In this technique, MR images arereformatted to reflect the changing image plane of a US transducer, andmodified in real-time to indicate tissue distortion detected with US.This confers the ability to image in real-time with ultrasound, but tostill visualize lesions to the extent possible with MRI.

The marker placement device's position would be known from both the USdata and from a separate position tracking system. A representation ofthe device's location would be overlaid on the reformatted MR imagedescribed above. Markers may then be positioned relative to a lesion asit appears on MRI, but whose morphology is being updated based on USmonitoring.

According to the invention, these markers do not have to be made of MRcompatible materials. In one embodiment, they are constructed ofmaterials and geometries that are easily identified on US images (highlyUS reflective scattering). In another embodiment, these markers are madeof MR compatible materials so that their positions may be verifiedrelative to the lesion enhancement pattern on subsequent MR imagingprocedures (e.g. supine MR imaging may be preferable, in order to locatemarkers with the patient in the position used for surgery). Thisprocedure is demonstrated in FIG. 22 and FIG. 23 and in the flowchartshown in FIG. 30. Marker placement under mammography, ultrasound and MRIhave been presented in recent years, however multiple marker placement,and MR/US combined marker placement have not been presented in the priorart. FIG. 22 shows the positioning of multiple clips 500 at a lesion 502in a breast 458 by devices 452 guided by transducer 450 from a medialperspective. FIG. 23 shows an image of the devices inserting the markersfrom the physician's point of view.

FIG. 24 a shows that hybrid needle 542 (e.g., tissue ablation probe suchas a cryotherapy probe) may be delivered to a lesion 502 in a breast458, with delivery made in multiple positions based on MRI imaging. InFIG. 24 b, it is indicated that therapy can be monitored with US and/orcorresponding MR data as a US image 545 or reformatted MRI image 544. Alesion 502 may be segmented from the MRI data through various means,with probe position 542 and tissue architecture demonstrated in thereformatted MR image 544. The corresponding features may be present inthe corresponding US image as an US visible lesion 545 with or withoutfused MRI data to assist in validation of lesion position and/or probeposition.

Example 12 Hybrid Monitoring of Therapy Delivery

According to the invention, this system can be used to accommodate avariety of tissue investigation or ablation devices, such as invasiveultrasound tissue ablation devices, RF heating devices, cryotherapysystems, local delivery of chemotherapeutic agents, optical ablation(lasers), optical photodynamic systems, or any other tissue destructiontechnique. Monitoring of these therapies may be performed using theposition-tracked US transducer with imaging techniques such as standardgrayscale imaging, Doppler imaging to characterize in blood flow, ormeasurement of temperature as a function of changes in the speed ofsound and attenuation properties. Grayscale US imaging has been shown tobe a reliable technique to monitor delivery of cryoablative therapy, asthe ice formed in the tissue is readily detected as a highlyUS-reflective surface. The utility of US as the monitoring and deviceguidance technique is to provide more accurate device placement, as wellas limit the amount of expensive MR imaging time required to monitorlong treatments (thermal ablation of tumors may be up to ninety minutesin duration). This procedure is demonstrated in FIGS. 24 a and b and inthe flowchart shown in FIG. 31.

Minimally invasive tissue ablation techniques have been presented inrecent years for breast, brain prostate and liver therapy. Limited usefor breast cancer ablation has been presented. No prior art has beenpresented involving a combined MRI detection and US guidance strategyfor these therapies. MRI detection and MRI monitoring has been used forcryoablation and laser ablation of breast tumors, without US guidanceand monitoring. Differing from the presented invention is a systemdeveloped by TxSonics Inc using MRI guidance to detect tumors andmonitor therapy, and high-power US to ablate tumors. Only through amodification of the approaches taken in inventions thus far can anappropriate embodiment be realized. Only the use of US-guidance tomonitor ablation therapies can decrease the expensive MRI time requiredto perform these procedures making them more economically appropriate.The preceding specific embodiments are illustrative of the practice ofthe present invention. It is to be understood that other embodimentsknown to those skilled in the art or disclosed herein may be employedwithout departing from the invention or the scope of the claims.

The practice of the invention as described above provides the followingsystems functions:

Technique for medial/lateral MR-guided delivery of needle to the breastusing straight or angled needle trajectories.

Techniques for MR/US hybrid biopsy

Technique to co-register MR and US images

-   -   Reformatting of MR image to correspond to US image    -   Correction of US image for speed of sound variations    -   Correction of image co-registration errors    -   Registration of common anatomical features used to calculate        co-registration accuracy

Delivery of a variety of needle gauge sizes as well as various minimallyinvasive treatment devices.

Positioning of multiple marking coils into the breast to defineboundaries of lesions through a single incision.

According to the invention, the following functions are provided withminimal reconfiguration of the apparatus:

1) High quality breast images in bilateral screening and unilateralfollow-up examinations using various MR coil configurations can be usedfor both procedures, and comprising an optimal breast compressionstrategy as well as optimizing access to the breast by the MRtechnician;

2) MR-guided localization, including medial or lateral biopsy, withoutprior knowledge of lesion location;

3) MR-guided multiple biopsy, including medial or lateral biopsy, withor without angulated needle approach;

4) MR-guided marker placement for improved surgical excision, under MRguidance, wherein a marker is positioned at the edges of the lesion asdefined by MRI. The procedure would be similar to the MRI-guided biopsyprocedure, however, a marker would be placed into the breast ratherremoving a sample of tissue. This may be conducted in conjunction withMR-guided biopsy, in conjunction with MR-guided needle localization.

5) MR-guided positioning of devices other than biopsy needles, includingtissue investigation or ablation devices, such as invasive ultrasoundtissue ablation devices, RF-heating applicators, cryoablative systems,miniature imaging coils, or optical photodynamic systems. According tothe invention, monitoring of these devices may be done using the MRsystem to measure heating or cooling patterns during therapy. In thecase of the optical systems, treatment region may be determined usingother techniques (i.e. T2-weighted contrast sequences).

6) MR-US fusion imaging, wherein real-time US data can be used toposition a device accurately into the lesion. This may be done using USexclusively when the lesion is visible on the US image, or using acombination of the MRI and US data fused using a variety of techniques.This strategy involves detecting the lesion using MRI, then removing thepatient from the MR magnet room to perform US imaging. According to theinvention, US imaging could involve a number of procedures

a. US imaging—simple use of the US so as to identify the lesion anddetermine its malignancy status. Identification of the lesion in thismanner could also act to provide lesion location and US properties withwhich the lesion may be identified for subsequent US-guided biopsy withthe patient removed from the biopsy apparatus. Knowledge of the USfeatures of the lesion could lead to easy identification of the lesionin a follow-up US examination. In cases where the lesion is difficult toidentify in the US image, the option to view the lesion as a fusionimage may assist in visualization.

b. Hybrid biopsy—this technique involves the use of the interventionalUS imaging membrane. This procedure requires stereotactic positioning ofthe US transducer in conjunction with free-hand delivery of the biopsyneedle. This may be augmented by the use of a fused MR/US data set, andwith or without the use of position-tracked US transducer and biopsyneedle. Markers can be superimposed onto the MR/US fused dataset in sucha way that the needle is easily identified on the MR/US fused image set,and in a way that the presented MR/US image updates to reflect theposition of the US transducer.

c. Hybrid marker placement. Based on the procedure above, except that aMR and US-visible marker is implanted in the breast. This results inmore accurate marker placement and reduces the amount of time spend inthe MR-magnet room.

d. Hybrid treatment. The hybrid device delivery technique may also beused to deliver devices other than biopsy needles and marker placementdevices such as tissue investigation or ablation devices. In this caseit is advantageous to monitor the therapy using US. This offers theability to improve the accuracy of the delivery and reduces the amountof time required for MR imaging. Again, this can be used with either thecombined MR/US images, or using only the US images if the lesion can beconfidently identified on the US image. The use of the fused MR/US datais beneficial when MRI provides better definition of tumor boundaries.

According to the invention, numerous techniques and methods can be usedto enable the practice of the various embodiments of the invention, asillustrated by the following specific examples:

Stereotactic positioning of needle/US transducer based on MRcoordinates:

Specification to deliver needle in straight (e.g. medial-lateral)orientation.

Specification of angulated needle delivery:

-   -   ability to select shortest needle paths, or desired needle        angle.    -   ability to eliminate occluded areas behind fenestrated        constraint plates    -   ability to identify guide needle position on MR images to ensure        that the chest wall will not be punctured during biopsy        acquisition

Specification of exact US transducer orientation and position, withtransducer mounted horizontally or vertically, under various constraints(minimal distance, selected orientation, etc.)

US transducer position tracking co-registered with breast frame ofreference:

Ability to determine transducer frame of reference relative to breastframe of reference. This enables the device plane to correspond with theMRI coordinates.

Uses of tracking position of US imaging plane:

-   -   Calculating corresponding plane from 3D MR data set (creating        virtual US image composed of reformatted MR data) will        correspond to US image position and orientation.    -   distance to lesion through-plane will be determined and shown        relative to virtual US image.    -   position of lesion center on US image will be identified.    -   MR data can be combined with the virtual US image to form a        fused MR/US image.    -   Segmentation of MR lesion from contrast-enhanced data will be        superimposed on the virtual US image to form a composite image.    -   Other auditory, tactile and visual cues may be used to guide        free-hand US transducer movement, enabling the user to operate        the system with or without a view of the US image.

Means of displaying position information about an interventional device:

-   -   a device's position may be tracked and an indication of its        position superimposed over an acquired image (i.e. tracking a        biopsy needle and superimposing an image of the device on the        co-registered MR, US, or fused MR/US images.

Integration of images and position tracking data to validate US and MRimage co-registration:

-   -   use of landmarks identified on US and MR images to confirm that        the MR image is aligned with the US image    -   use of image processing techniques and image acquisition        techniques to better identify common landmarks on both imaging        modalities. (i.e. breast parachymal patterns, vessels, cysts).    -   Method to quantify the similarity of two modalities. Means of        presenting the result to the operator.    -   Means of correcting the registration between the two modalities:        -   Speed of sound correction.

Use the MRI data to determine composition of the breast, use known speedof sound values for the appropriate tissues and correct the US image.

-   -   Gradient warp shifts.

Correct for large errors due to gradient warp in the MR imaging system.

-   -   Position or registration error due to patient motion.

Relies on operator identification of similar features on bothmodalities. Once selected, the user may displace one image set to matchthe other, or may use automated image processing algorithms for thispurpose.

As discussed herein, the benefits of the invention include, but are notlimited to:

System that can be used for breast imaging and multiple interventionfunctions.

Improved access to the entire breast volume for imaging andintervention.

Improved breast immobilization through full compression of breast(including volume near chest wall).

Improved breast compression technique for operator ease of use.

Improved probe delivery using MRI guidance:

More accurate probe delivery—angled delivery provided greater access.

Multiple target sampling through a single incision point.

Flexibility in the selection of biopsy approach (medial or lateral) tominimize trauma to the breast

Real-time US guided probe delivery through hybrid technique.

US guided sampling in the fringe field or even in another procedureroom.

Flexibility in the selection of biopsy approach (medial or lateral) tominimize trauma to the breast and distance of breast tissue traversedfor US imaging.

Ability to obtain many tissue samples through one small skin incision.

Ability to use standard interventional devices under US guidance, notlimited to equipment that is MR compatible, thus reducing disposableequipment costs and permitting use of superior, non-MR-compatibledevices.

Separation of MR imaging and biopsy procedure into two stages that canbe performed in different locations using one dedicated transportstretcher, thus freeing the MR facility and its own dedicated patienttransport stretcher for the next patient.

The foregoing description of the invention is not intended to describeevery object, feature, advantage, and implementation of the presentinvention. While the description of the embodiments of the invention isfocused on applications for breast imaging, it will be understood bythose skilled in the art that the present invention has utility toapplications elsewhere in the body. The primary differences would relateessentially to the geometry of the frames, which would hold the needleentry plate and the US plate.

All patents and printed publications referenced herein are herebyincorporated by reference into the specification hereof, each in itsrespective entirety.

1. An apparatus for volumetric imaging and ultrasound imaging of ananatomy of interest in a patient, the apparatus comprising: a patientsupport structure; a first immobilization device coupled to the patientsupport structure and configured to constrain the anatomy of interest ina selected position and conformation during both of a volumetric imagingexam and an ultrasound imaging exam; and a first deformable membranecoupled to the first immobilization device adjacent the anatomy ofinterest and constructed from a substantially ultrasound-transparentmaterial.
 2. The apparatus of claim 1, wherein the first immobilizationdevice comprises an immobilization frame defining a window, and thefirst deformable membrane covers at least a portion of the window suchthat ultrasound imaging of the anatomy of interest may be performedthrough the first deformable membrane.
 3. The apparatus of claim 1,wherein the first deformable membrane is of a thickness selected toallow puncturing or cutting of the first deformable membrane by astandard medical instrument.
 4. The apparatus of claim 1, furthercomprising a plurality of fiducial markers coupled to the firstimmobilization device, wherein the fiducial markers are constructed froma material visible on images reconstructed from data acquired during thevolumetric imaging.
 5. The apparatus of claim 1, further comprising asecond immobilization device, wherein the first immobilization deviceand the second immobilization device are translatably positionable onopposite sides of a breast, and are configured to compress the breast bydecreasing the distance between the first and second immobilizationdevice.
 6. The apparatus of claim 5, further comprising a seconddeformable membrane coupled to the second immobilization device andconstructed from a substantially ultrasound-transparent material.
 7. Theapparatus of claim 1, further comprising: a mechanical stage coupled tothe patient support; and a holder coupled to the mechanical stage andconfigured for holding an ultrasound transducer, the mechanical stageand the holder being configured to provide a plurality of degrees offreedom for positioning the ultrasound transducer.
 8. A method forvolumetric imaging and ultrasound imaging of an anatomy of interest in apatient, the method comprising the steps of: constraining the anatomy ofinterest in a fixed position and conformation using an immobilizationdevice; coupling a first deformable membrane comprising a substantiallyultrasound-transparent material to the immobilization device; performinga volumetric imaging exam to acquire volumetric imaging data;reconstructing an image from the volumetric imaging data; and performingan ultrasound imaging exam to acquire an ultrasound image through thefirst deformable membrane.
 9. The method of claim 8, further comprisingthe step of deforming the first deformable membrane to increase an areaof contact between the first deformable membrane and the anatomy ofinterest.
 10. The method of claim 8, further comprising the steps of:determining a coordinate transformation between a reference framecorresponding to the volumetric imaging exam and a reference framecorresponding to the ultrasound imaging exam;
 11. The method of claim10, wherein the step of determining the coordinate transformationcomprises the steps of: identifying on the image a known position on theimmobilization device; and determining the position and orientation ofthe ultrasound transducer relative to the known position.
 12. The methodof claim 10, wherein the step of determining a coordinate transformationcomprises the step of identifying an anatomical landmark in both the atleast one image and in the ultrasound images.
 13. The method of claim10, wherein the image reconstructed from the volumetric data is from thesame plane and location as the ultrasound image.
 14. The method of claim13, further comprising the step of displaying the ultrasound imageside-by-side with the image.
 15. The method of claim 13, furthercomprising the step of correlating the field of view for the ultrasoundimage and the image.
 16. The method of claim 13, further comprising thestep of coregistering the image and the ultrasound image to correctimage errors.
 17. The method of claim 13, further comprising the step ofcreating a fusion image from the ultrasound image and the image.
 18. Themethod of claim 10, further comprising the steps of: identifying alocation of interest in the image; determining coordinates of thelocation of interest in the reference frame corresponding to thevolumetric imaging exam.
 19. The method of claim 18, further comprisingthe step of: using the coordinate transformation to position and orientthe ultrasound transducer at a location and orientation such that aplane defined by the beam of the ultrasound transducer includes thelocation of interest.
 20. The method of claim 18, further comprising thestep of: using the coordinate transformation to position and orient amedical instrument to target the location of interest.
 21. The method ofclaim 20, further comprising the step of: displaying the position andorientation of the medical instrument on the at least one image.
 22. Themethod of claim 21, wherein the medical instrument is a device forperforming at least one of a biopsy, a marker placement, a cryotherapytreatment, an RF heating treatment, an invasive ultrasound tissueablation, a local delivery of a chemotherapeutic agent, an opticalablation, and an optical photodynamic therapy.
 23. The method of claim11, wherein the step of determining the position and orientation of theultrasound transducer relative to the fiducial markers comprises using afreehand tracking device coupled to the ultrasound transducer.
 24. Themethod of claim 19, wherein the step of using the coordinatetransformation to position and orient the ultrasound transducer at alocation and orientation such that a plane defined by the beam of theultrasound transducer includes the location of interest comprises usinga freehand tracking device coupled to the ultrasound transducer.